diff --git a/pkg/wasm/lib/src/module.dart b/pkg/wasm/lib/src/module.dart
index 349757a9781..6de13995c0a 100644
--- a/pkg/wasm/lib/src/module.dart
+++ b/pkg/wasm/lib/src/module.dart
@@ -114,6 +114,7 @@ class WasmInstanceBuilder {
   late List<WasmImportDescriptor> _importDescs;
   Map<String, int> _importIndex;
   late Pointer<Pointer<WasmerExtern>> _imports;
+  Pointer<WasmerWasiEnv> _wasiEnv = nullptr;
 
   WasmInstanceBuilder(this._module) : _importIndex = {} {
     _importDescs = WasmRuntime().importDescriptors(_module._module);
@@ -174,6 +175,21 @@ class WasmInstanceBuilder {
     return this;
   }
 
+  /// Enable WASI and add the default WASI imports.
+  WasmInstanceBuilder enableWasi(
+      {bool captureStdout = false, bool captureStderr = false}) {
+    if (_wasiEnv != nullptr) {
+      throw Exception("WASI is already enabled.");
+    }
+    var runtime = WasmRuntime();
+    var config = runtime.newWasiConfig();
+    if (captureStdout) runtime.captureWasiStdout(config);
+    if (captureStderr) runtime.captureWasiStderr(config);
+    _wasiEnv = runtime.newWasiEnv(config);
+    runtime.getWasiImports(_module._store, _module._module, _wasiEnv, _imports);
+    return this;
+  }
+
   /// Build the module instance.
   WasmInstance build() {
     for (var i = 0; i < _importDescs.length; ++i) {
@@ -181,7 +197,7 @@ class WasmInstanceBuilder {
         throw Exception("Missing import: ${_importDescs[i]}");
       }
     }
-    return WasmInstance(_module, _imports);
+    return WasmInstance(_module, _imports, _wasiEnv);
   }
 }
 
@@ -190,9 +206,13 @@ class WasmInstance {
   WasmModule _module;
   Pointer<WasmerInstance> _instance;
   Pointer<WasmerMemory>? _exportedMemory;
+  Pointer<WasmerWasiEnv> _wasiEnv;
+  Stream<List<int>>? _stdout;
+  Stream<List<int>>? _stderr;
   Map<String, WasmFunction> _functions = {};
 
-  WasmInstance(this._module, Pointer<Pointer<WasmerExtern>> imports)
+  WasmInstance(
+      this._module, Pointer<Pointer<WasmerExtern>> imports, this._wasiEnv)
       : _instance = WasmRuntime()
             .instantiate(_module._store, _module._module, imports) {
     var runtime = WasmRuntime();
@@ -210,7 +230,11 @@ class WasmInstance {
             name, f, runtime.getArgTypes(ft), runtime.getReturnType(ft));
       } else if (kind == WasmerExternKindMemory) {
         // WASM currently allows only one memory per module.
-        _exportedMemory = runtime.externToMemory(e);
+        var mem = runtime.externToMemory(e);
+        _exportedMemory = mem;
+        if (_wasiEnv != nullptr) {
+          runtime.wasiEnvSetMemory(_wasiEnv as Pointer<WasmerWasiEnv>, mem);
+        }
       }
     }
   }
@@ -228,6 +252,24 @@ class WasmInstance {
     }
     return WasmMemory._fromExport(_exportedMemory as Pointer<WasmerMemory>);
   }
+
+  /// Returns a stream that reads from stdout. To use this, you must enable WASI
+  /// when instantiating the module, and set captureStdout to true.
+  Stream<List<int>> get stdout {
+    if (_wasiEnv == nullptr) {
+      throw Exception("Can't capture stdout without WASI enabled.");
+    }
+    return _stdout ??= WasmRuntime().getWasiStdoutStream(_wasiEnv);
+  }
+
+  /// Returns a stream that reads from stderr. To use this, you must enable WASI
+  /// when instantiating the module, and set captureStderr to true.
+  Stream<List<int>> get stderr {
+    if (_wasiEnv == nullptr) {
+      throw Exception("Can't capture stderr without WASI enabled.");
+    }
+    return _stderr ??= WasmRuntime().getWasiStderrStream(_wasiEnv);
+  }
 }
 
 /// WasmMemory contains the memory of a WasmInstance.
diff --git a/pkg/wasm/lib/src/runtime.dart b/pkg/wasm/lib/src/runtime.dart
index f3908915e78..e14bda073be 100644
--- a/pkg/wasm/lib/src/runtime.dart
+++ b/pkg/wasm/lib/src/runtime.dart
@@ -6,6 +6,7 @@
 // To regenerate the file, use the following command
 // "generate_ffi_boilerplate.py".
 
+import 'dart:async';
 import 'dart:convert';
 import 'dart:ffi';
 import 'dart:io';
@@ -58,6 +59,15 @@ class WasmRuntime {
 
   DynamicLibrary _lib;
   late Pointer<WasmerEngine> _engine;
+  late WasmerWasiConfigInheritStderrFn _wasi_config_inherit_stderr;
+  late WasmerWasiConfigInheritStdoutFn _wasi_config_inherit_stdout;
+  late WasmerWasiConfigNewFn _wasi_config_new;
+  late WasmerWasiEnvDeleteFn _wasi_env_delete;
+  late WasmerWasiEnvNewFn _wasi_env_new;
+  late WasmerWasiEnvReadStderrFn _wasi_env_read_stderr;
+  late WasmerWasiEnvReadStdoutFn _wasi_env_read_stdout;
+  late WasmerWasiEnvSetMemoryFn _wasi_env_set_memory;
+  late WasmerWasiGetImportsFn _wasi_get_imports;
   late WasmerByteVecDeleteFn _byte_vec_delete;
   late WasmerByteVecNewFn _byte_vec_new;
   late WasmerByteVecNewEmptyFn _byte_vec_new_empty;
@@ -120,11 +130,11 @@ class WasmRuntime {
   late WasmerValtypeVecNewFn _valtype_vec_new;
   late WasmerValtypeVecNewEmptyFn _valtype_vec_new_empty;
   late WasmerValtypeVecNewUninitializedFn _valtype_vec_new_uninitialized;
+  late WasmerWasmerLastErrorLengthFn _wasmer_last_error_length;
+  late WasmerWasmerLastErrorMessageFn _wasmer_last_error_message;
 
   factory WasmRuntime() {
-    WasmRuntime inst = _inst ?? WasmRuntime._init();
-    _inst = inst;
-    return inst;
+    return _inst ??= WasmRuntime._init();
   }
 
   static String _getLibName() {
@@ -165,6 +175,29 @@ class WasmRuntime {
 
   WasmRuntime._init()
       : _lib = DynamicLibrary.open(path.join(_getLibDir(), _getLibName())) {
+    _wasi_config_inherit_stderr = _lib.lookupFunction<
+        NativeWasmerWasiConfigInheritStderrFn,
+        WasmerWasiConfigInheritStderrFn>('wasi_config_inherit_stderr');
+    _wasi_config_inherit_stdout = _lib.lookupFunction<
+        NativeWasmerWasiConfigInheritStdoutFn,
+        WasmerWasiConfigInheritStdoutFn>('wasi_config_inherit_stdout');
+    _wasi_config_new =
+        _lib.lookupFunction<NativeWasmerWasiConfigNewFn, WasmerWasiConfigNewFn>(
+            'wasi_config_new');
+    _wasi_env_delete =
+        _lib.lookupFunction<NativeWasmerWasiEnvDeleteFn, WasmerWasiEnvDeleteFn>(
+            'wasi_env_delete');
+    _wasi_env_new =
+        _lib.lookupFunction<NativeWasmerWasiEnvNewFn, WasmerWasiEnvNewFn>(
+            'wasi_env_new');
+    _wasi_env_read_stderr = _lib.lookupFunction<NativeWasmerWasiEnvReadStderrFn,
+        WasmerWasiEnvReadStderrFn>('wasi_env_read_stderr');
+    _wasi_env_read_stdout = _lib.lookupFunction<NativeWasmerWasiEnvReadStdoutFn,
+        WasmerWasiEnvReadStdoutFn>('wasi_env_read_stdout');
+    _wasi_env_set_memory = _lib.lookupFunction<NativeWasmerWasiEnvSetMemoryFn,
+        WasmerWasiEnvSetMemoryFn>('wasi_env_set_memory');
+    _wasi_get_imports = _lib.lookupFunction<NativeWasmerWasiGetImportsFn,
+        WasmerWasiGetImportsFn>('wasi_get_imports');
     _byte_vec_delete =
         _lib.lookupFunction<NativeWasmerByteVecDeleteFn, WasmerByteVecDeleteFn>(
             'wasm_byte_vec_delete');
@@ -329,6 +362,12 @@ class WasmRuntime {
             NativeWasmerValtypeVecNewUninitializedFn,
             WasmerValtypeVecNewUninitializedFn>(
         'wasm_valtype_vec_new_uninitialized');
+    _wasmer_last_error_length = _lib.lookupFunction<
+        NativeWasmerWasmerLastErrorLengthFn,
+        WasmerWasmerLastErrorLengthFn>('wasmer_last_error_length');
+    _wasmer_last_error_message = _lib.lookupFunction<
+        NativeWasmerWasmerLastErrorMessageFn,
+        WasmerWasmerLastErrorMessageFn>('wasmer_last_error_message');
 
     _engine = _engine_new();
   }
@@ -351,11 +390,7 @@ class WasmRuntime {
     free(dataPtr);
     free(dataVec);
 
-    if (modulePtr == nullptr) {
-      throw Exception("Wasm module compile failed");
-    }
-
-    return modulePtr;
+    return _checkNotEqual(modulePtr, nullptr, "Wasm module compile failed.");
   }
 
   List<WasmExportDescriptor> exportDescriptors(Pointer<WasmerModule> module) {
@@ -399,12 +434,8 @@ class WasmRuntime {
 
   Pointer<WasmerInstance> instantiate(Pointer<WasmerStore> store,
       Pointer<WasmerModule> module, Pointer<Pointer<WasmerExtern>> imports) {
-    var instancePtr = _instance_new(store, module, imports, nullptr);
-    if (instancePtr == nullptr) {
-      throw Exception("Wasm module instantiation failed");
-    }
-
-    return instancePtr;
+    return _checkNotEqual(_instance_new(store, module, imports, nullptr),
+        nullptr, "Wasm module instantiation failed.");
   }
 
   Pointer<WasmerExternVec> exports(Pointer<WasmerInstance> instancePtr) {
@@ -464,19 +495,13 @@ class WasmRuntime {
     limPtr.ref.max = maxPages ?? wasm_limits_max_default;
     var memType = _memorytype_new(limPtr);
     free(limPtr);
-    Pointer<WasmerMemory> memPtr = _memory_new(store, memType);
-
-    if (memPtr == nullptr) {
-      throw Exception("Failed to create memory");
-    }
-    return memPtr;
+    return _checkNotEqual(
+        _memory_new(store, memType), nullptr, "Failed to create memory.");
   }
 
   void growMemory(Pointer<WasmerMemory> memory, int deltaPages) {
-    var result = _memory_grow(memory, deltaPages);
-    if (result == 0) {
-      throw Exception("Failed to grow memory");
-    }
+    _checkNotEqual(
+        _memory_grow(memory, deltaPages), 0, "Failed to grow memory.");
   }
 
   int memoryLength(Pointer<WasmerMemory> memory) {
@@ -497,9 +522,89 @@ class WasmRuntime {
         store, funcType, func.cast(), env.cast(), finalizer.cast());
   }
 
+  Pointer<WasmerWasiConfig> newWasiConfig() {
+    var name = allocate<Uint8>();
+    name[0] = 0;
+    var config = _wasi_config_new(name);
+    free(name);
+    return _checkNotEqual(config, nullptr, "Failed to create WASI config.");
+  }
+
+  void captureWasiStdout(Pointer<WasmerWasiConfig> config) {
+    _wasi_config_inherit_stdout(config);
+  }
+
+  void captureWasiStderr(Pointer<WasmerWasiConfig> config) {
+    _wasi_config_inherit_stderr(config);
+  }
+
+  Pointer<WasmerWasiEnv> newWasiEnv(Pointer<WasmerWasiConfig> config) {
+    return _checkNotEqual(
+        _wasi_env_new(config), nullptr, "Failed to create WASI environment.");
+  }
+
+  void wasiEnvSetMemory(
+      Pointer<WasmerWasiEnv> env, Pointer<WasmerMemory> memory) {
+    _wasi_env_set_memory(env, memory);
+  }
+
+  void getWasiImports(Pointer<WasmerStore> store, Pointer<WasmerModule> mod,
+      Pointer<WasmerWasiEnv> env, Pointer<Pointer<WasmerExtern>> imports) {
+    _checkNotEqual(_wasi_get_imports(store, mod, env, imports), 0,
+        "Failed to fill WASI imports.");
+  }
+
+  Stream<List<int>> getWasiStdoutStream(Pointer<WasmerWasiEnv> env) {
+    return Stream.fromIterable(_WasiStreamIterable(env, _wasi_env_read_stdout));
+  }
+
+  Stream<List<int>> getWasiStderrStream(Pointer<WasmerWasiEnv> env) {
+    return Stream.fromIterable(_WasiStreamIterable(env, _wasi_env_read_stderr));
+  }
+
+  String _getLastError() {
+    var length = _wasmer_last_error_length();
+    var buf = allocate<Uint8>(count: length);
+    _wasmer_last_error_message(buf, length);
+    String message = utf8.decode(buf.asTypedList(length));
+    free(buf);
+    return message;
+  }
+
+  T _checkNotEqual<T>(T x, T y, String errorMessage) {
+    if (x == y) {
+      throw Exception("$errorMessage\n${_getLastError()}");
+    }
+    return x;
+  }
+
   static String getSignatureString(
       String name, List<int> argTypes, int returnType) {
     return "${wasmerValKindName(returnType)} $name" +
         "(${argTypes.map(wasmerValKindName).join(", ")})";
   }
 }
+
+class _WasiStreamIterator implements Iterator<List<int>> {
+  static final int _bufferLength = 1024;
+  Pointer<WasmerWasiEnv> _env;
+  Function _reader;
+  Pointer<Uint8> _buf = allocate<Uint8>(count: _bufferLength);
+  int _length = 0;
+  _WasiStreamIterator(this._env, this._reader) {}
+
+  bool moveNext() {
+    _length = _reader(_env, _buf, _bufferLength);
+    return true;
+  }
+
+  List<int> get current => _buf.asTypedList(_length);
+}
+
+class _WasiStreamIterable extends Iterable<List<int>> {
+  Pointer<WasmerWasiEnv> _env;
+  Function _reader;
+  _WasiStreamIterable(this._env, this._reader) {}
+  @override
+  Iterator<List<int>> get iterator => _WasiStreamIterator(_env, _reader);
+}
diff --git a/pkg/wasm/lib/src/tools/generate_ffi_boilerplate.py b/pkg/wasm/lib/src/tools/generate_ffi_boilerplate.py
index 94ed9652c45..906cea52706 100755
--- a/pkg/wasm/lib/src/tools/generate_ffi_boilerplate.py
+++ b/pkg/wasm/lib/src/tools/generate_ffi_boilerplate.py
@@ -33,13 +33,23 @@ def ptrWrap(t, n):
     return t
 
 
+def removePrefix(t):
+    assert (t.startswith('wasm_') or t.startswith('wasi_') or
+            t.startswith('wasmer_'))
+    return t[(5 if t.startswith('wasm_') else 0):]
+
+
+def addPrefix(t):
+    if t.startswith('wasi_') or t.startswith('wasmer_'):
+        return t
+    return 'wasm_' + t
+
+
 def getDartType(t, i):
     if t in predefTypes:
-        t = predefTypes[t][i]
-    else:
-        assert (t.startswith('wasm_') and t.endswith('_t'))
-        t = 'Wasmer' + camel(t[5:-2])
-    return t
+        return predefTypes[t][i]
+    assert (t.endswith('_t'))
+    return 'Wasmer' + camel(removePrefix(t[:-2]))
 
 
 def dartArgType(a, i):
@@ -54,13 +64,11 @@ def dartFnType(r, a, i):
 
 
 def dartFnTypeName(n):
-    assert (n.startswith('wasm_'))
-    return camel(n[5:])
+    return camel(removePrefix(n))
 
 
 def dartFnMembName(n):
-    assert (n.startswith('wasm_'))
-    return n[4:]
+    return '_' + removePrefix(n)
 
 
 def nativeTypeToFfi(n):
@@ -77,10 +85,10 @@ def getFns():
             yield name, retType, args
 
 
-opaqueTypeTemplate = '''// wasm_%s_t
+opaqueTypeTemplate = '''// %s_t
 class Wasmer%s extends Struct {}'''
 
-vecTypeTemplate = '''// wasm_%s_vec_t
+vecTypeTemplate = '''// %s_vec_t
 class Wasmer%sVec extends Struct {
   @Uint64()
   external int length;
@@ -103,12 +111,13 @@ typedef Wasmer%sFn = %s;'''
 
 def getWasmerApi():
     return ('\n\n'.join([
-        opaqueTypeTemplate % (t, camel(t)) for t in sorted(opaqueTypes)
+        opaqueTypeTemplate % (addPrefix(t), camel(t))
+        for t in sorted(opaqueTypes)
     ]) + '\n\n' + '\n\n'.join([
-        vecTypeTemplate %
-        (t, camel(t),
-         ('Pointer<%s>' if ptr else '%s') % nativeTypeToFfi('wasm_%s_t' % t),
-         (byteVecToStringTemplate if t == 'byte' else ''))
+        vecTypeTemplate % (addPrefix(t), camel(t),
+                           ('Pointer<%s>' if ptr else '%s') % nativeTypeToFfi(
+                               '%s_t' % addPrefix(t)),
+                           (byteVecToStringTemplate if t == 'byte' else ''))
         for t, ptr in sorted(vecTypes.items())
     ]) + '\n' + '\n'.join([
         fnApiTemplate %
@@ -189,38 +198,41 @@ def addFn(sig):
     retType = parseType(ret)
     args = [parseType(a) for a in argpack.split(',') if len(a.strip()) > 0]
     for _, t in args + [retType]:
-        if t not in predefTypes and t[5:-2] not in opaqueTypes and t[
-                5:-6] not in vecTypes:
+        if t not in predefTypes and removePrefix(
+                t[:-2]) not in opaqueTypes and removePrefix(
+                    t[:-6]) not in vecTypes:
             print('Missing type: ' + t)
     fns.append((name, retType, args))
 
 
 def declareOwn(name):
     opaqueTypes.add(name)
-    addFn('void wasm_%s_delete(wasm_%s_t*)' % (name, name))
+    n = addPrefix(name)
+    addFn('void %s_delete(%s_t*)' % (n, n))
 
 
 def declareVec(name, storePtr):
     vecTypes[name] = storePtr
-    addFn('void wasm_%s_vec_new_empty(wasm_%s_vec_t* out)' % (name, name))
-    addFn('void wasm_%s_vec_new_uninitialized(wasm_%s_vec_t* out, size_t)' %
-          (name, name))
-    addFn('void wasm_%s_vec_new(wasm_%s_vec_t* out, size_t, wasm_%s_t %s[])' %
-          (name, name, name, '*' if storePtr else ''))
-    addFn('void wasm_%s_vec_copy(wasm_%s_vec_t* out, const wasm_%s_vec_t*)' %
-          (name, name, name))
-    addFn('void wasm_%s_vec_delete(wasm_%s_vec_t*)' % (name, name))
+    n = addPrefix(name)
+    addFn('void %s_vec_new_empty(%s_vec_t* out)' % (n, n))
+    addFn('void %s_vec_new_uninitialized(%s_vec_t* out, size_t)' % (n, n))
+    addFn('void %s_vec_new(%s_vec_t* out, size_t, %s_t %s[])' %
+          (n, n, n, '*' if storePtr else ''))
+    addFn('void %s_vec_copy(%s_vec_t* out, const %s_vec_t*)' % (n, n, n))
+    addFn('void %s_vec_delete(%s_vec_t*)' % (n, n))
 
 
 def declareType(name, withCopy=True):
     declareOwn(name)
     declareVec(name, True)
     if withCopy:
-        addFn('wasm_%s_t* wasm_%s_copy(wasm_%s_t*)' % (name, name, name))
+        n = addPrefix(name)
+        addFn('%s_t* %s_copy(%s_t*)' % (n, n, n))
 
 
 predefinedType('void', 'Void', 'void')
 predefinedType('bool', 'Uint8', 'int')
+predefinedType('int', 'Int64', 'int')
 predefinedType('byte_t', 'Uint8', 'int')
 predefinedType('wasm_byte_t', 'Uint8', 'int')
 predefinedType('uint8_t', 'Uint8', 'int')
@@ -228,6 +240,8 @@ predefinedType('uint16_t', 'Uint16', 'int')
 predefinedType('uint32_t', 'Uint32', 'int')
 predefinedType('uint64_t', 'Uint64', 'int')
 predefinedType('size_t', 'Uint64', 'int')
+predefinedType('uintptr_t', 'Uint64', 'int')
+predefinedType('intptr_t', 'Int64', 'int')
 predefinedType('int8_t', 'Int8', 'int')
 predefinedType('int16_t', 'Int16', 'int')
 predefinedType('int32_t', 'Int32', 'int')
@@ -239,6 +253,8 @@ predefinedType('wasm_val_t', 'WasmerVal', 'WasmerVal')
 
 declareOwn('engine')
 declareOwn('store')
+declareOwn('wasi_config')
+declareOwn('wasi_env')
 declareVec('byte', False)
 declareVec('val', False)
 declareType('importtype')
@@ -291,6 +307,16 @@ WASM_API_EXTERN const wasm_valtype_vec_t* wasm_functype_results(const wasm_funct
 WASM_API_EXTERN own wasm_func_t* wasm_func_new_with_env( wasm_store_t*, const wasm_functype_t* type, void* fn, void* env, void *finalizer);
 WASM_API_EXTERN own wasm_trap_t* wasm_func_call(const wasm_func_t*, const wasm_val_t args[], wasm_val_t results[]);
 WASM_API_EXTERN wasm_valkind_t wasm_valtype_kind(const wasm_valtype_t*);
+wasi_config_t* wasi_config_new(const uint8_t* program_name);
+wasi_env_t* wasi_env_new(wasi_config_t* config);
+bool wasi_get_imports(const wasm_store_t* store, const wasm_module_t* module, const wasi_env_t* wasi_env, wasm_extern_t** imports);
+int wasmer_last_error_message(uint8_t* buffer, int length);
+int wasmer_last_error_length();
+void wasi_env_set_memory(wasi_env_t* env, const wasm_memory_t* memory);
+void wasi_config_inherit_stdout(wasi_config_t* config);
+void wasi_config_inherit_stderr(wasi_config_t* config);
+intptr_t wasi_env_read_stderr(wasi_env_t* env, uint8_t* buffer, uintptr_t buffer_len);
+intptr_t wasi_env_read_stdout(wasi_env_t* env, uint8_t* buffer, uintptr_t buffer_len);
 '''
 for f in rawFns.split('\n'):
     if len(f.strip()) > 0:
@@ -312,6 +338,7 @@ unusedFns = {
     'wasm_val_vec_new_uninitialized',
     'wasm_valtype_copy',
     'wasm_valtype_vec_copy',
+    'wasi_config_delete',
 }
 
 genDoc = '''// This file has been automatically generated. Please do not edit it manually.
diff --git a/pkg/wasm/lib/src/tools/runtime_template.dart b/pkg/wasm/lib/src/tools/runtime_template.dart
index 280edb5ee10..981da8d23a0 100644
--- a/pkg/wasm/lib/src/tools/runtime_template.dart
+++ b/pkg/wasm/lib/src/tools/runtime_template.dart
@@ -4,6 +4,7 @@
 
 /* <GEN_DOC> */
 
+import 'dart:async';
 import 'dart:convert';
 import 'dart:ffi';
 import 'dart:io';
@@ -59,9 +60,7 @@ class WasmRuntime {
 /* <RUNTIME_MEMB> */
 
   factory WasmRuntime() {
-    WasmRuntime inst = _inst ?? WasmRuntime._init();
-    _inst = inst;
-    return inst;
+    return _inst ??= WasmRuntime._init();
   }
 
   static String _getLibName() {
@@ -125,11 +124,7 @@ class WasmRuntime {
     free(dataPtr);
     free(dataVec);
 
-    if (modulePtr == nullptr) {
-      throw Exception("Wasm module compile failed");
-    }
-
-    return modulePtr;
+    return _checkNotEqual(modulePtr, nullptr, "Wasm module compile failed.");
   }
 
   List<WasmExportDescriptor> exportDescriptors(Pointer<WasmerModule> module) {
@@ -173,12 +168,8 @@ class WasmRuntime {
 
   Pointer<WasmerInstance> instantiate(Pointer<WasmerStore> store,
       Pointer<WasmerModule> module, Pointer<Pointer<WasmerExtern>> imports) {
-    var instancePtr = _instance_new(store, module, imports, nullptr);
-    if (instancePtr == nullptr) {
-      throw Exception("Wasm module instantiation failed");
-    }
-
-    return instancePtr;
+    return _checkNotEqual(_instance_new(store, module, imports, nullptr),
+        nullptr, "Wasm module instantiation failed.");
   }
 
   Pointer<WasmerExternVec> exports(Pointer<WasmerInstance> instancePtr) {
@@ -238,19 +229,13 @@ class WasmRuntime {
     limPtr.ref.max = maxPages ?? wasm_limits_max_default;
     var memType = _memorytype_new(limPtr);
     free(limPtr);
-    Pointer<WasmerMemory> memPtr = _memory_new(store, memType);
-
-    if (memPtr == nullptr) {
-      throw Exception("Failed to create memory");
-    }
-    return memPtr;
+    return _checkNotEqual(
+        _memory_new(store, memType), nullptr, "Failed to create memory.");
   }
 
   void growMemory(Pointer<WasmerMemory> memory, int deltaPages) {
-    var result = _memory_grow(memory, deltaPages);
-    if (result == 0) {
-      throw Exception("Failed to grow memory");
-    }
+    _checkNotEqual(
+        _memory_grow(memory, deltaPages), 0, "Failed to grow memory.");
   }
 
   int memoryLength(Pointer<WasmerMemory> memory) {
@@ -271,9 +256,89 @@ class WasmRuntime {
         store, funcType, func.cast(), env.cast(), finalizer.cast());
   }
 
+  Pointer<WasmerWasiConfig> newWasiConfig() {
+    var name = allocate<Uint8>();
+    name[0] = 0;
+    var config = _wasi_config_new(name);
+    free(name);
+    return _checkNotEqual(config, nullptr, "Failed to create WASI config.");
+  }
+
+  void captureWasiStdout(Pointer<WasmerWasiConfig> config) {
+    _wasi_config_inherit_stdout(config);
+  }
+
+  void captureWasiStderr(Pointer<WasmerWasiConfig> config) {
+    _wasi_config_inherit_stderr(config);
+  }
+
+  Pointer<WasmerWasiEnv> newWasiEnv(Pointer<WasmerWasiConfig> config) {
+    return _checkNotEqual(
+        _wasi_env_new(config), nullptr, "Failed to create WASI environment.");
+  }
+
+  void wasiEnvSetMemory(
+      Pointer<WasmerWasiEnv> env, Pointer<WasmerMemory> memory) {
+    _wasi_env_set_memory(env, memory);
+  }
+
+  void getWasiImports(Pointer<WasmerStore> store, Pointer<WasmerModule> mod,
+      Pointer<WasmerWasiEnv> env, Pointer<Pointer<WasmerExtern>> imports) {
+    _checkNotEqual(_wasi_get_imports(store, mod, env, imports), 0,
+        "Failed to fill WASI imports.");
+  }
+
+  Stream<List<int>> getWasiStdoutStream(Pointer<WasmerWasiEnv> env) {
+    return Stream.fromIterable(_WasiStreamIterable(env, _wasi_env_read_stdout));
+  }
+
+  Stream<List<int>> getWasiStderrStream(Pointer<WasmerWasiEnv> env) {
+    return Stream.fromIterable(_WasiStreamIterable(env, _wasi_env_read_stderr));
+  }
+
+  String _getLastError() {
+    var length = _wasmer_last_error_length();
+    var buf = allocate<Uint8>(count: length);
+    _wasmer_last_error_message(buf, length);
+    String message = utf8.decode(buf.asTypedList(length));
+    free(buf);
+    return message;
+  }
+
+  T _checkNotEqual<T>(T x, T y, String errorMessage) {
+    if (x == y) {
+      throw Exception("$errorMessage\n${_getLastError()}");
+    }
+    return x;
+  }
+
   static String getSignatureString(
       String name, List<int> argTypes, int returnType) {
     return "${wasmerValKindName(returnType)} $name" +
         "(${argTypes.map(wasmerValKindName).join(", ")})";
   }
 }
+
+class _WasiStreamIterator implements Iterator<List<int>> {
+  static final int _bufferLength = 1024;
+  Pointer<WasmerWasiEnv> _env;
+  Function _reader;
+  Pointer<Uint8> _buf = allocate<Uint8>(count: _bufferLength);
+  int _length = 0;
+  _WasiStreamIterator(this._env, this._reader) {}
+
+  bool moveNext() {
+    _length = _reader(_env, _buf, _bufferLength);
+    return true;
+  }
+
+  List<int> get current => _buf.asTypedList(_length);
+}
+
+class _WasiStreamIterable extends Iterable<List<int>> {
+  Pointer<WasmerWasiEnv> _env;
+  Function _reader;
+  _WasiStreamIterable(this._env, this._reader) {}
+  @override
+  Iterator<List<int>> get iterator => _WasiStreamIterator(_env, _reader);
+}
diff --git a/pkg/wasm/lib/src/wasmer_api.dart b/pkg/wasm/lib/src/wasmer_api.dart
index 95f244f7bcd..c8e55c7eb14 100644
--- a/pkg/wasm/lib/src/wasmer_api.dart
+++ b/pkg/wasm/lib/src/wasmer_api.dart
@@ -157,6 +157,12 @@ class WasmerTrap extends Struct {}
 // wasm_valtype_t
 class WasmerValtype extends Struct {}
 
+// wasi_config_t
+class WasmerWasiConfig extends Struct {}
+
+// wasi_env_t
+class WasmerWasiEnv extends Struct {}
+
 // wasm_byte_vec_t
 class WasmerByteVec extends Struct {
   @Uint64()
@@ -208,6 +214,64 @@ class WasmerValtypeVec extends Struct {
   external Pointer<Pointer<WasmerValtype>> data;
 }
 
+// wasi_config_inherit_stderr
+typedef NativeWasmerWasiConfigInheritStderrFn = Void Function(
+    Pointer<WasmerWasiConfig>);
+typedef WasmerWasiConfigInheritStderrFn = void Function(
+    Pointer<WasmerWasiConfig>);
+
+// wasi_config_inherit_stdout
+typedef NativeWasmerWasiConfigInheritStdoutFn = Void Function(
+    Pointer<WasmerWasiConfig>);
+typedef WasmerWasiConfigInheritStdoutFn = void Function(
+    Pointer<WasmerWasiConfig>);
+
+// wasi_config_new
+typedef NativeWasmerWasiConfigNewFn = Pointer<WasmerWasiConfig> Function(
+    Pointer<Uint8>);
+typedef WasmerWasiConfigNewFn = Pointer<WasmerWasiConfig> Function(
+    Pointer<Uint8>);
+
+// wasi_env_delete
+typedef NativeWasmerWasiEnvDeleteFn = Void Function(Pointer<WasmerWasiEnv>);
+typedef WasmerWasiEnvDeleteFn = void Function(Pointer<WasmerWasiEnv>);
+
+// wasi_env_new
+typedef NativeWasmerWasiEnvNewFn = Pointer<WasmerWasiEnv> Function(
+    Pointer<WasmerWasiConfig>);
+typedef WasmerWasiEnvNewFn = Pointer<WasmerWasiEnv> Function(
+    Pointer<WasmerWasiConfig>);
+
+// wasi_env_read_stderr
+typedef NativeWasmerWasiEnvReadStderrFn = Int64 Function(
+    Pointer<WasmerWasiEnv>, Pointer<Uint8>, Uint64);
+typedef WasmerWasiEnvReadStderrFn = int Function(
+    Pointer<WasmerWasiEnv>, Pointer<Uint8>, int);
+
+// wasi_env_read_stdout
+typedef NativeWasmerWasiEnvReadStdoutFn = Int64 Function(
+    Pointer<WasmerWasiEnv>, Pointer<Uint8>, Uint64);
+typedef WasmerWasiEnvReadStdoutFn = int Function(
+    Pointer<WasmerWasiEnv>, Pointer<Uint8>, int);
+
+// wasi_env_set_memory
+typedef NativeWasmerWasiEnvSetMemoryFn = Void Function(
+    Pointer<WasmerWasiEnv>, Pointer<WasmerMemory>);
+typedef WasmerWasiEnvSetMemoryFn = void Function(
+    Pointer<WasmerWasiEnv>, Pointer<WasmerMemory>);
+
+// wasi_get_imports
+typedef NativeWasmerWasiGetImportsFn = Uint8 Function(
+    Pointer<WasmerStore>,
+    Pointer<WasmerModule>,
+    Pointer<WasmerWasiEnv>,
+    Pointer<Pointer<WasmerExtern>>);
+typedef WasmerWasiGetImportsFn = int Function(
+    Pointer<WasmerStore>,
+    Pointer<WasmerModule>,
+    Pointer<WasmerWasiEnv>,
+    Pointer<Pointer<WasmerExtern>>);
+
 // wasm_byte_vec_delete
 typedef NativeWasmerByteVecDeleteFn = Void Function(Pointer<WasmerByteVec>);
 typedef WasmerByteVecDeleteFn = void Function(Pointer<WasmerByteVec>);
@@ -548,3 +612,12 @@ typedef NativeWasmerValtypeVecNewUninitializedFn = Void Function(
     Pointer<WasmerValtypeVec>, Uint64);
 typedef WasmerValtypeVecNewUninitializedFn = void Function(
     Pointer<WasmerValtypeVec>, int);
+
+// wasmer_last_error_length
+typedef NativeWasmerWasmerLastErrorLengthFn = Int64 Function();
+typedef WasmerWasmerLastErrorLengthFn = int Function();
+
+// wasmer_last_error_message
+typedef NativeWasmerWasmerLastErrorMessageFn = Int64 Function(
+    Pointer<Uint8>, Int64);
+typedef WasmerWasmerLastErrorMessageFn = int Function(Pointer<Uint8>, int);
diff --git a/tests/lib/wasm/fn_import_error_test.dart b/tests/lib/wasm/fn_import_error_test.dart
index 844c9bfb9f9..aeca278487d 100644
--- a/tests/lib/wasm/fn_import_error_test.dart
+++ b/tests/lib/wasm/fn_import_error_test.dart
@@ -27,25 +27,42 @@ void main() {
   var mod = WasmModule(data);
 
   // Valid instantiation.
-  var inst = mod.instantiate()
-    .addFunction(
-        "env", "someFn", (int a, int b, num c, double d) => 123).build();
+  var inst = mod
+      .instantiate()
+      .addFunction("env", "someFn", (int a, int b, num c, double d) => 123)
+      .build();
 
   // Missing imports.
-  Expect.throws(() => mod.instantiate().build(), (Exception e) => "$e".contains("Missing import"));
+  Expect.throws(() => mod.instantiate().build(),
+      (Exception e) => "$e".contains("Missing import"));
 
   // Wrong kind of import.
-  Expect.throws(() => mod.instantiate().addMemory("env", "someFn", mod.createMemory(10)), (Exception e) => "$e".contains("Import is not a memory"));
+  Expect.throws(
+      () => mod.instantiate().addMemory("env", "someFn", mod.createMemory(10)),
+      (Exception e) => "$e".contains("Import is not a memory"));
 
   // Wrong namespace.
-  Expect.throws(() => mod.instantiate().addFunction("foo", "someFn", (int a, int b, num c, double d) => 123).build(), (Exception e) => "$e".contains("Import not found"));
+  Expect.throws(
+      () => mod
+          .instantiate()
+          .addFunction("foo", "someFn", (int a, int b, num c, double d) => 123)
+          .build(),
+      (Exception e) => "$e".contains("Import not found"));
 
   // Wrong name.
-  Expect.throws(() => mod.instantiate().addFunction("env", "otherFn", (int a, int b, num c, double d) => 123).build(), (Exception e) => "$e".contains("Import not found"));
+  Expect.throws(
+      () => mod
+          .instantiate()
+          .addFunction("env", "otherFn", (int a, int b, num c, double d) => 123)
+          .build(),
+      (Exception e) => "$e".contains("Import not found"));
 
   // Already filled.
-  Expect.throws(() => mod.instantiate()
-    .addFunction("env", "someFn", (int a, int b, num c, double d) => 123)
-    .addFunction("env", "someFn", (int a, int b, num c, double d) => 456)
-    .build(), (Exception e) => "$e".contains("Import already filled"));
+  Expect.throws(
+      () => mod
+          .instantiate()
+          .addFunction("env", "someFn", (int a, int b, num c, double d) => 123)
+          .addFunction("env", "someFn", (int a, int b, num c, double d) => 456)
+          .build(),
+      (Exception e) => "$e".contains("Import already filled"));
 }
diff --git a/tests/lib/wasm/hello_wasi_test.dart b/tests/lib/wasm/hello_wasi_test.dart
new file mode 100644
index 00000000000..d862b8968b1
--- /dev/null
+++ b/tests/lib/wasm/hello_wasi_test.dart
@@ -0,0 +1,184 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Variant of hello_world_test that uses the default WASI imports.
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+import "package:wasm/wasm.dart";
+import "dart:convert";
+import "dart:typed_data";
+
+void main() async {
+  asyncStart();
+
+  // Hello world module generated by emscripten+WASI. Exports a function like
+  // `void _start()`, and prints using `int fd_write(int, int, int, int)`.
+  var data = Uint8List.fromList([
+    0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x33, 0x09, 0x60,
+    0x03, 0x7f, 0x7f, 0x7f, 0x01, 0x7f, 0x60, 0x04, 0x7f, 0x7f, 0x7f, 0x7f,
+    0x01, 0x7f, 0x60, 0x00, 0x00, 0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x60,
+    0x01, 0x7f, 0x01, 0x7f, 0x60, 0x03, 0x7f, 0x7e, 0x7f, 0x01, 0x7e, 0x60,
+    0x00, 0x01, 0x7f, 0x60, 0x01, 0x7f, 0x00, 0x60, 0x03, 0x7f, 0x7f, 0x7f,
+    0x00, 0x02, 0x1a, 0x01, 0x0d, 0x77, 0x61, 0x73, 0x69, 0x5f, 0x75, 0x6e,
+    0x73, 0x74, 0x61, 0x62, 0x6c, 0x65, 0x08, 0x66, 0x64, 0x5f, 0x77, 0x72,
+    0x69, 0x74, 0x65, 0x00, 0x01, 0x03, 0x0f, 0x0e, 0x03, 0x04, 0x00, 0x03,
+    0x02, 0x07, 0x05, 0x04, 0x03, 0x06, 0x02, 0x02, 0x08, 0x00, 0x04, 0x05,
+    0x01, 0x70, 0x01, 0x04, 0x04, 0x05, 0x06, 0x01, 0x01, 0x80, 0x02, 0x80,
+    0x02, 0x06, 0x09, 0x01, 0x7f, 0x01, 0x41, 0xc0, 0x95, 0xc0, 0x02, 0x0b,
+    0x07, 0x2e, 0x04, 0x06, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x02, 0x00,
+    0x11, 0x5f, 0x5f, 0x77, 0x61, 0x73, 0x6d, 0x5f, 0x63, 0x61, 0x6c, 0x6c,
+    0x5f, 0x63, 0x74, 0x6f, 0x72, 0x73, 0x00, 0x05, 0x04, 0x6d, 0x61, 0x69,
+    0x6e, 0x00, 0x04, 0x06, 0x5f, 0x73, 0x74, 0x61, 0x72, 0x74, 0x00, 0x0b,
+    0x09, 0x09, 0x01, 0x00, 0x41, 0x01, 0x0b, 0x03, 0x08, 0x0e, 0x07, 0x0a,
+    0xae, 0x0c, 0x0e, 0xbf, 0x01, 0x01, 0x05, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x04, 0x02, 0x40, 0x20, 0x01, 0x28, 0x02, 0x10, 0x22, 0x02, 0x04, 0x7f,
+    0x20, 0x02, 0x05, 0x20, 0x01, 0x10, 0x02, 0x0d, 0x01, 0x20, 0x01, 0x28,
+    0x02, 0x10, 0x0b, 0x20, 0x01, 0x28, 0x02, 0x14, 0x22, 0x05, 0x6b, 0x20,
+    0x00, 0x49, 0x04, 0x40, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20, 0x00, 0x20,
+    0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x0f, 0x0b, 0x02, 0x40, 0x20,
+    0x01, 0x2c, 0x00, 0x4b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x20, 0x00, 0x21,
+    0x03, 0x03, 0x40, 0x20, 0x03, 0x22, 0x02, 0x45, 0x0d, 0x01, 0x20, 0x02,
+    0x41, 0x7f, 0x6a, 0x22, 0x03, 0x41, 0x80, 0x08, 0x6a, 0x2d, 0x00, 0x00,
+    0x41, 0x0a, 0x47, 0x0d, 0x00, 0x0b, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20,
+    0x02, 0x20, 0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x22, 0x03, 0x20,
+    0x02, 0x49, 0x0d, 0x01, 0x20, 0x00, 0x20, 0x02, 0x6b, 0x21, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0x08, 0x6a, 0x21, 0x04, 0x20, 0x01, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x02, 0x21, 0x06, 0x0b, 0x20, 0x05, 0x20, 0x04, 0x20,
+    0x00, 0x10, 0x03, 0x1a, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x14, 0x20,
+    0x00, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x06, 0x6a, 0x21, 0x03,
+    0x0b, 0x20, 0x03, 0x0b, 0x59, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x20, 0x00,
+    0x2d, 0x00, 0x4a, 0x22, 0x01, 0x41, 0x7f, 0x6a, 0x20, 0x01, 0x72, 0x3a,
+    0x00, 0x4a, 0x20, 0x00, 0x28, 0x02, 0x00, 0x22, 0x01, 0x41, 0x08, 0x71,
+    0x04, 0x40, 0x20, 0x00, 0x20, 0x01, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x7f, 0x0f, 0x0b, 0x20, 0x00, 0x42, 0x00, 0x37, 0x02, 0x04, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02, 0x1c, 0x20,
+    0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01, 0x20, 0x00,
+    0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x41, 0x00, 0x0b, 0x82, 0x04,
+    0x01, 0x03, 0x7f, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x4f, 0x04, 0x40,
+    0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x10, 0x0d, 0x20, 0x00, 0x0f, 0x0b,
+    0x20, 0x00, 0x20, 0x02, 0x6a, 0x21, 0x03, 0x02, 0x40, 0x20, 0x00, 0x20,
+    0x01, 0x73, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x02, 0x40, 0x20, 0x02,
+    0x41, 0x01, 0x48, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b,
+    0x20, 0x00, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02, 0x03, 0x40, 0x20, 0x02, 0x20,
+    0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a,
+    0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02, 0x20, 0x03, 0x4f,
+    0x0d, 0x01, 0x20, 0x02, 0x41, 0x03, 0x71, 0x0d, 0x00, 0x0b, 0x0b, 0x02,
+    0x40, 0x20, 0x03, 0x41, 0x7c, 0x71, 0x22, 0x04, 0x41, 0xc0, 0x00, 0x49,
+    0x0d, 0x00, 0x20, 0x02, 0x20, 0x04, 0x41, 0x40, 0x6a, 0x22, 0x05, 0x4b,
+    0x0d, 0x00, 0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36,
+    0x02, 0x00, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x04, 0x36, 0x02, 0x04,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x08, 0x36, 0x02, 0x08, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x0c, 0x36, 0x02, 0x0c, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x10, 0x36, 0x02, 0x10, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x14, 0x36, 0x02, 0x14, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x18, 0x36,
+    0x02, 0x18, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x1c, 0x36, 0x02, 0x1c,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x20, 0x36, 0x02, 0x20, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x24, 0x36, 0x02, 0x24, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x28, 0x36, 0x02, 0x28, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x2c, 0x36, 0x02, 0x2c, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x30, 0x36,
+    0x02, 0x30, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x34, 0x36, 0x02, 0x34,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x38, 0x36, 0x02, 0x38, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x3c, 0x36, 0x02, 0x3c, 0x20, 0x01, 0x41, 0x40,
+    0x6b, 0x21, 0x01, 0x20, 0x02, 0x41, 0x40, 0x6b, 0x22, 0x02, 0x20, 0x05,
+    0x4d, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x04, 0x4f, 0x0d, 0x01,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36, 0x02, 0x00,
+    0x20, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x04, 0x6a,
+    0x22, 0x02, 0x20, 0x04, 0x49, 0x0d, 0x00, 0x0b, 0x0c, 0x01, 0x0b, 0x20,
+    0x03, 0x41, 0x04, 0x49, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01,
+    0x0b, 0x20, 0x03, 0x41, 0x7c, 0x6a, 0x22, 0x04, 0x20, 0x00, 0x49, 0x04,
+    0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x3a, 0x00, 0x01, 0x20, 0x02,
+    0x20, 0x01, 0x2d, 0x00, 0x02, 0x3a, 0x00, 0x02, 0x20, 0x02, 0x20, 0x01,
+    0x2d, 0x00, 0x03, 0x3a, 0x00, 0x03, 0x20, 0x01, 0x41, 0x04, 0x6a, 0x21,
+    0x01, 0x20, 0x02, 0x41, 0x04, 0x6a, 0x22, 0x02, 0x20, 0x04, 0x4d, 0x0d,
+    0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x03, 0x49, 0x04, 0x40, 0x03, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01,
+    0x41, 0x01, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02,
+    0x20, 0x03, 0x47, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x00, 0x0b, 0x06, 0x00,
+    0x10, 0x0c, 0x41, 0x00, 0x0b, 0x03, 0x00, 0x01, 0x0b, 0x7e, 0x01, 0x03,
+    0x7f, 0x23, 0x00, 0x41, 0x10, 0x6b, 0x22, 0x01, 0x24, 0x00, 0x20, 0x01,
+    0x41, 0x0a, 0x3a, 0x00, 0x0f, 0x02, 0x40, 0x20, 0x00, 0x28, 0x02, 0x10,
+    0x22, 0x02, 0x45, 0x04, 0x40, 0x20, 0x00, 0x10, 0x02, 0x0d, 0x01, 0x20,
+    0x00, 0x28, 0x02, 0x10, 0x21, 0x02, 0x0b, 0x02, 0x40, 0x20, 0x00, 0x28,
+    0x02, 0x14, 0x22, 0x03, 0x20, 0x02, 0x4f, 0x0d, 0x00, 0x20, 0x00, 0x2c,
+    0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00, 0x20, 0x03, 0x41,
+    0x01, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x03, 0x41, 0x0a, 0x3a, 0x00, 0x00,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x20, 0x01, 0x41, 0x0f, 0x6a, 0x41, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x41, 0x01, 0x47, 0x0d,
+    0x00, 0x20, 0x01, 0x2d, 0x00, 0x0f, 0x1a, 0x0b, 0x20, 0x01, 0x41, 0x10,
+    0x6a, 0x24, 0x00, 0x0b, 0x04, 0x00, 0x42, 0x00, 0x0b, 0x04, 0x00, 0x41,
+    0x00, 0x0b, 0x31, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x21, 0x02, 0x20, 0x02,
+    0x02, 0x7f, 0x20, 0x01, 0x28, 0x02, 0x4c, 0x41, 0x7f, 0x4c, 0x04, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x10, 0x01, 0x0c, 0x01, 0x0b, 0x20, 0x02, 0x20,
+    0x01, 0x10, 0x01, 0x0b, 0x22, 0x01, 0x46, 0x04, 0x40, 0x20, 0x00, 0x0f,
+    0x0b, 0x20, 0x01, 0x0b, 0x62, 0x01, 0x03, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x00, 0x03, 0x40, 0x20, 0x00, 0x22, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x00,
+    0x20, 0x01, 0x28, 0x02, 0x00, 0x22, 0x02, 0x41, 0x7f, 0x73, 0x20, 0x02,
+    0x41, 0xff, 0xfd, 0xfb, 0x77, 0x6a, 0x71, 0x41, 0x80, 0x81, 0x82, 0x84,
+    0x78, 0x71, 0x45, 0x0d, 0x00, 0x0b, 0x02, 0x40, 0x20, 0x02, 0x41, 0xff,
+    0x01, 0x71, 0x45, 0x04, 0x40, 0x20, 0x01, 0x21, 0x00, 0x0c, 0x01, 0x0b,
+    0x03, 0x40, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x21, 0x02, 0x20, 0x01, 0x41,
+    0x01, 0x6a, 0x22, 0x00, 0x21, 0x01, 0x20, 0x02, 0x0d, 0x00, 0x0b, 0x0b,
+    0x20, 0x00, 0x41, 0x80, 0x08, 0x6b, 0x0b, 0x0c, 0x00, 0x02, 0x7f, 0x41,
+    0x00, 0x41, 0x00, 0x10, 0x04, 0x0b, 0x1a, 0x0b, 0x66, 0x01, 0x02, 0x7f,
+    0x41, 0x90, 0x08, 0x28, 0x02, 0x00, 0x22, 0x00, 0x28, 0x02, 0x4c, 0x41,
+    0x00, 0x4e, 0x04, 0x7f, 0x41, 0x01, 0x05, 0x20, 0x01, 0x0b, 0x1a, 0x02,
+    0x40, 0x41, 0x7f, 0x41, 0x00, 0x10, 0x0a, 0x22, 0x01, 0x20, 0x01, 0x20,
+    0x00, 0x10, 0x09, 0x47, 0x1b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x02, 0x40,
+    0x20, 0x00, 0x2d, 0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00,
+    0x28, 0x02, 0x14, 0x22, 0x01, 0x20, 0x00, 0x28, 0x02, 0x10, 0x4f, 0x0d,
+    0x00, 0x20, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a, 0x36, 0x02, 0x14, 0x20,
+    0x01, 0x41, 0x0a, 0x3a, 0x00, 0x00, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x10,
+    0x06, 0x0b, 0x0b, 0x3d, 0x01, 0x01, 0x7f, 0x20, 0x02, 0x04, 0x40, 0x03,
+    0x40, 0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0xc0, 0x00, 0x49, 0x1b, 0x22, 0x03, 0x10, 0x03, 0x21,
+    0x00, 0x20, 0x01, 0x41, 0x80, 0x40, 0x6b, 0x21, 0x01, 0x20, 0x00, 0x41,
+    0x80, 0x40, 0x6b, 0x21, 0x00, 0x20, 0x02, 0x20, 0x03, 0x6b, 0x22, 0x02,
+    0x0d, 0x00, 0x0b, 0x0b, 0x0b, 0xb1, 0x02, 0x01, 0x06, 0x7f, 0x23, 0x00,
+    0x41, 0x20, 0x6b, 0x22, 0x03, 0x24, 0x00, 0x20, 0x03, 0x20, 0x00, 0x28,
+    0x02, 0x1c, 0x22, 0x04, 0x36, 0x02, 0x10, 0x20, 0x00, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x03, 0x20, 0x02, 0x36, 0x02, 0x1c, 0x20, 0x03, 0x20,
+    0x01, 0x36, 0x02, 0x18, 0x20, 0x03, 0x20, 0x05, 0x20, 0x04, 0x6b, 0x22,
+    0x01, 0x36, 0x02, 0x14, 0x20, 0x01, 0x20, 0x02, 0x6a, 0x21, 0x06, 0x41,
+    0x02, 0x21, 0x05, 0x20, 0x03, 0x41, 0x10, 0x6a, 0x21, 0x01, 0x03, 0x40,
+    0x02, 0x40, 0x02, 0x7f, 0x20, 0x06, 0x02, 0x7f, 0x20, 0x00, 0x28, 0x02,
+    0x3c, 0x20, 0x01, 0x20, 0x05, 0x20, 0x03, 0x41, 0x0c, 0x6a, 0x10, 0x00,
+    0x04, 0x40, 0x20, 0x03, 0x41, 0x7f, 0x36, 0x02, 0x0c, 0x41, 0x7f, 0x0c,
+    0x01, 0x0b, 0x20, 0x03, 0x28, 0x02, 0x0c, 0x0b, 0x22, 0x04, 0x46, 0x04,
+    0x40, 0x20, 0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02,
+    0x1c, 0x20, 0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x20, 0x02, 0x0c,
+    0x01, 0x0b, 0x20, 0x04, 0x41, 0x7f, 0x4a, 0x0d, 0x01, 0x20, 0x00, 0x41,
+    0x00, 0x36, 0x02, 0x1c, 0x20, 0x00, 0x42, 0x00, 0x37, 0x03, 0x10, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x00, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x00, 0x20, 0x05, 0x41, 0x02, 0x46, 0x0d, 0x00, 0x1a, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x04, 0x6b, 0x0b, 0x21, 0x04, 0x20, 0x03, 0x41,
+    0x20, 0x6a, 0x24, 0x00, 0x20, 0x04, 0x0f, 0x0b, 0x20, 0x01, 0x41, 0x08,
+    0x6a, 0x20, 0x01, 0x20, 0x04, 0x20, 0x01, 0x28, 0x02, 0x04, 0x22, 0x07,
+    0x4b, 0x22, 0x08, 0x1b, 0x22, 0x01, 0x20, 0x04, 0x20, 0x07, 0x41, 0x00,
+    0x20, 0x08, 0x1b, 0x6b, 0x22, 0x07, 0x20, 0x01, 0x28, 0x02, 0x00, 0x6a,
+    0x36, 0x02, 0x00, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x04, 0x20, 0x07,
+    0x6b, 0x36, 0x02, 0x04, 0x20, 0x06, 0x20, 0x04, 0x6b, 0x21, 0x06, 0x20,
+    0x05, 0x20, 0x08, 0x6b, 0x21, 0x05, 0x0c, 0x00, 0x00, 0x0b, 0x00, 0x0b,
+    0x0b, 0x4d, 0x06, 0x00, 0x41, 0x80, 0x08, 0x0b, 0x12, 0x68, 0x65, 0x6c,
+    0x6c, 0x6f, 0x2c, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x21, 0x00, 0x00,
+    0x00, 0x18, 0x04, 0x00, 0x41, 0x98, 0x08, 0x0b, 0x01, 0x05, 0x00, 0x41,
+    0xa4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xbc, 0x08, 0x0b, 0x0e, 0x02,
+    0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0xb8, 0x04, 0x00, 0x00, 0x00,
+    0x04, 0x00, 0x41, 0xd4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xe3, 0x08,
+    0x0b, 0x05, 0x0a, 0xff, 0xff, 0xff, 0xff,
+  ]);
+
+  var inst =
+      WasmModule(data).instantiate().enableWasi(captureStdout: true).build();
+
+  var fn = inst.lookupFunction("_start");
+  fn();
+  var out = utf8.decode(await inst.stdout.first);
+  Expect.equals("hello, world!\n", out);
+  asyncEnd();
+}
diff --git a/tests/lib/wasm/wasi_error_test.dart b/tests/lib/wasm/wasi_error_test.dart
new file mode 100644
index 00000000000..8418dad832a
--- /dev/null
+++ b/tests/lib/wasm/wasi_error_test.dart
@@ -0,0 +1,204 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test the errors that can be thrown by WASI.
+
+import "package:expect/expect.dart";
+import "package:wasm/wasm.dart";
+import "dart:typed_data";
+
+void main() {
+  // Empty wasm module.
+  var emptyModuleData = Uint8List.fromList(
+      [0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x06, 0x81, 0x00, 0x00]);
+
+  // Failed to fill WASI imports (the empty module was not built with WASI).
+  Expect.throws(() => WasmModule(emptyModuleData).instantiate().enableWasi(),
+      (Exception e) => "$e".contains("Failed to fill WASI imports"));
+
+  // Hello world module generated by emscripten+WASI. Exports a function like
+  // `void _start()`, and prints using `int fd_write(int, int, int, int)`.
+  var helloWorldData = Uint8List.fromList([
+    0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x33, 0x09, 0x60,
+    0x03, 0x7f, 0x7f, 0x7f, 0x01, 0x7f, 0x60, 0x04, 0x7f, 0x7f, 0x7f, 0x7f,
+    0x01, 0x7f, 0x60, 0x00, 0x00, 0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x60,
+    0x01, 0x7f, 0x01, 0x7f, 0x60, 0x03, 0x7f, 0x7e, 0x7f, 0x01, 0x7e, 0x60,
+    0x00, 0x01, 0x7f, 0x60, 0x01, 0x7f, 0x00, 0x60, 0x03, 0x7f, 0x7f, 0x7f,
+    0x00, 0x02, 0x1a, 0x01, 0x0d, 0x77, 0x61, 0x73, 0x69, 0x5f, 0x75, 0x6e,
+    0x73, 0x74, 0x61, 0x62, 0x6c, 0x65, 0x08, 0x66, 0x64, 0x5f, 0x77, 0x72,
+    0x69, 0x74, 0x65, 0x00, 0x01, 0x03, 0x0f, 0x0e, 0x03, 0x04, 0x00, 0x03,
+    0x02, 0x07, 0x05, 0x04, 0x03, 0x06, 0x02, 0x02, 0x08, 0x00, 0x04, 0x05,
+    0x01, 0x70, 0x01, 0x04, 0x04, 0x05, 0x06, 0x01, 0x01, 0x80, 0x02, 0x80,
+    0x02, 0x06, 0x09, 0x01, 0x7f, 0x01, 0x41, 0xc0, 0x95, 0xc0, 0x02, 0x0b,
+    0x07, 0x2e, 0x04, 0x06, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x02, 0x00,
+    0x11, 0x5f, 0x5f, 0x77, 0x61, 0x73, 0x6d, 0x5f, 0x63, 0x61, 0x6c, 0x6c,
+    0x5f, 0x63, 0x74, 0x6f, 0x72, 0x73, 0x00, 0x05, 0x04, 0x6d, 0x61, 0x69,
+    0x6e, 0x00, 0x04, 0x06, 0x5f, 0x73, 0x74, 0x61, 0x72, 0x74, 0x00, 0x0b,
+    0x09, 0x09, 0x01, 0x00, 0x41, 0x01, 0x0b, 0x03, 0x08, 0x0e, 0x07, 0x0a,
+    0xae, 0x0c, 0x0e, 0xbf, 0x01, 0x01, 0x05, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x04, 0x02, 0x40, 0x20, 0x01, 0x28, 0x02, 0x10, 0x22, 0x02, 0x04, 0x7f,
+    0x20, 0x02, 0x05, 0x20, 0x01, 0x10, 0x02, 0x0d, 0x01, 0x20, 0x01, 0x28,
+    0x02, 0x10, 0x0b, 0x20, 0x01, 0x28, 0x02, 0x14, 0x22, 0x05, 0x6b, 0x20,
+    0x00, 0x49, 0x04, 0x40, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20, 0x00, 0x20,
+    0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x0f, 0x0b, 0x02, 0x40, 0x20,
+    0x01, 0x2c, 0x00, 0x4b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x20, 0x00, 0x21,
+    0x03, 0x03, 0x40, 0x20, 0x03, 0x22, 0x02, 0x45, 0x0d, 0x01, 0x20, 0x02,
+    0x41, 0x7f, 0x6a, 0x22, 0x03, 0x41, 0x80, 0x08, 0x6a, 0x2d, 0x00, 0x00,
+    0x41, 0x0a, 0x47, 0x0d, 0x00, 0x0b, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20,
+    0x02, 0x20, 0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x22, 0x03, 0x20,
+    0x02, 0x49, 0x0d, 0x01, 0x20, 0x00, 0x20, 0x02, 0x6b, 0x21, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0x08, 0x6a, 0x21, 0x04, 0x20, 0x01, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x02, 0x21, 0x06, 0x0b, 0x20, 0x05, 0x20, 0x04, 0x20,
+    0x00, 0x10, 0x03, 0x1a, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x14, 0x20,
+    0x00, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x06, 0x6a, 0x21, 0x03,
+    0x0b, 0x20, 0x03, 0x0b, 0x59, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x20, 0x00,
+    0x2d, 0x00, 0x4a, 0x22, 0x01, 0x41, 0x7f, 0x6a, 0x20, 0x01, 0x72, 0x3a,
+    0x00, 0x4a, 0x20, 0x00, 0x28, 0x02, 0x00, 0x22, 0x01, 0x41, 0x08, 0x71,
+    0x04, 0x40, 0x20, 0x00, 0x20, 0x01, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x7f, 0x0f, 0x0b, 0x20, 0x00, 0x42, 0x00, 0x37, 0x02, 0x04, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02, 0x1c, 0x20,
+    0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01, 0x20, 0x00,
+    0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x41, 0x00, 0x0b, 0x82, 0x04,
+    0x01, 0x03, 0x7f, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x4f, 0x04, 0x40,
+    0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x10, 0x0d, 0x20, 0x00, 0x0f, 0x0b,
+    0x20, 0x00, 0x20, 0x02, 0x6a, 0x21, 0x03, 0x02, 0x40, 0x20, 0x00, 0x20,
+    0x01, 0x73, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x02, 0x40, 0x20, 0x02,
+    0x41, 0x01, 0x48, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b,
+    0x20, 0x00, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02, 0x03, 0x40, 0x20, 0x02, 0x20,
+    0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a,
+    0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02, 0x20, 0x03, 0x4f,
+    0x0d, 0x01, 0x20, 0x02, 0x41, 0x03, 0x71, 0x0d, 0x00, 0x0b, 0x0b, 0x02,
+    0x40, 0x20, 0x03, 0x41, 0x7c, 0x71, 0x22, 0x04, 0x41, 0xc0, 0x00, 0x49,
+    0x0d, 0x00, 0x20, 0x02, 0x20, 0x04, 0x41, 0x40, 0x6a, 0x22, 0x05, 0x4b,
+    0x0d, 0x00, 0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36,
+    0x02, 0x00, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x04, 0x36, 0x02, 0x04,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x08, 0x36, 0x02, 0x08, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x0c, 0x36, 0x02, 0x0c, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x10, 0x36, 0x02, 0x10, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x14, 0x36, 0x02, 0x14, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x18, 0x36,
+    0x02, 0x18, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x1c, 0x36, 0x02, 0x1c,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x20, 0x36, 0x02, 0x20, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x24, 0x36, 0x02, 0x24, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x28, 0x36, 0x02, 0x28, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x2c, 0x36, 0x02, 0x2c, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x30, 0x36,
+    0x02, 0x30, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x34, 0x36, 0x02, 0x34,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x38, 0x36, 0x02, 0x38, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x3c, 0x36, 0x02, 0x3c, 0x20, 0x01, 0x41, 0x40,
+    0x6b, 0x21, 0x01, 0x20, 0x02, 0x41, 0x40, 0x6b, 0x22, 0x02, 0x20, 0x05,
+    0x4d, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x04, 0x4f, 0x0d, 0x01,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36, 0x02, 0x00,
+    0x20, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x04, 0x6a,
+    0x22, 0x02, 0x20, 0x04, 0x49, 0x0d, 0x00, 0x0b, 0x0c, 0x01, 0x0b, 0x20,
+    0x03, 0x41, 0x04, 0x49, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01,
+    0x0b, 0x20, 0x03, 0x41, 0x7c, 0x6a, 0x22, 0x04, 0x20, 0x00, 0x49, 0x04,
+    0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x3a, 0x00, 0x01, 0x20, 0x02,
+    0x20, 0x01, 0x2d, 0x00, 0x02, 0x3a, 0x00, 0x02, 0x20, 0x02, 0x20, 0x01,
+    0x2d, 0x00, 0x03, 0x3a, 0x00, 0x03, 0x20, 0x01, 0x41, 0x04, 0x6a, 0x21,
+    0x01, 0x20, 0x02, 0x41, 0x04, 0x6a, 0x22, 0x02, 0x20, 0x04, 0x4d, 0x0d,
+    0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x03, 0x49, 0x04, 0x40, 0x03, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01,
+    0x41, 0x01, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02,
+    0x20, 0x03, 0x47, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x00, 0x0b, 0x06, 0x00,
+    0x10, 0x0c, 0x41, 0x00, 0x0b, 0x03, 0x00, 0x01, 0x0b, 0x7e, 0x01, 0x03,
+    0x7f, 0x23, 0x00, 0x41, 0x10, 0x6b, 0x22, 0x01, 0x24, 0x00, 0x20, 0x01,
+    0x41, 0x0a, 0x3a, 0x00, 0x0f, 0x02, 0x40, 0x20, 0x00, 0x28, 0x02, 0x10,
+    0x22, 0x02, 0x45, 0x04, 0x40, 0x20, 0x00, 0x10, 0x02, 0x0d, 0x01, 0x20,
+    0x00, 0x28, 0x02, 0x10, 0x21, 0x02, 0x0b, 0x02, 0x40, 0x20, 0x00, 0x28,
+    0x02, 0x14, 0x22, 0x03, 0x20, 0x02, 0x4f, 0x0d, 0x00, 0x20, 0x00, 0x2c,
+    0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00, 0x20, 0x03, 0x41,
+    0x01, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x03, 0x41, 0x0a, 0x3a, 0x00, 0x00,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x20, 0x01, 0x41, 0x0f, 0x6a, 0x41, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x41, 0x01, 0x47, 0x0d,
+    0x00, 0x20, 0x01, 0x2d, 0x00, 0x0f, 0x1a, 0x0b, 0x20, 0x01, 0x41, 0x10,
+    0x6a, 0x24, 0x00, 0x0b, 0x04, 0x00, 0x42, 0x00, 0x0b, 0x04, 0x00, 0x41,
+    0x00, 0x0b, 0x31, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x21, 0x02, 0x20, 0x02,
+    0x02, 0x7f, 0x20, 0x01, 0x28, 0x02, 0x4c, 0x41, 0x7f, 0x4c, 0x04, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x10, 0x01, 0x0c, 0x01, 0x0b, 0x20, 0x02, 0x20,
+    0x01, 0x10, 0x01, 0x0b, 0x22, 0x01, 0x46, 0x04, 0x40, 0x20, 0x00, 0x0f,
+    0x0b, 0x20, 0x01, 0x0b, 0x62, 0x01, 0x03, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x00, 0x03, 0x40, 0x20, 0x00, 0x22, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x00,
+    0x20, 0x01, 0x28, 0x02, 0x00, 0x22, 0x02, 0x41, 0x7f, 0x73, 0x20, 0x02,
+    0x41, 0xff, 0xfd, 0xfb, 0x77, 0x6a, 0x71, 0x41, 0x80, 0x81, 0x82, 0x84,
+    0x78, 0x71, 0x45, 0x0d, 0x00, 0x0b, 0x02, 0x40, 0x20, 0x02, 0x41, 0xff,
+    0x01, 0x71, 0x45, 0x04, 0x40, 0x20, 0x01, 0x21, 0x00, 0x0c, 0x01, 0x0b,
+    0x03, 0x40, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x21, 0x02, 0x20, 0x01, 0x41,
+    0x01, 0x6a, 0x22, 0x00, 0x21, 0x01, 0x20, 0x02, 0x0d, 0x00, 0x0b, 0x0b,
+    0x20, 0x00, 0x41, 0x80, 0x08, 0x6b, 0x0b, 0x0c, 0x00, 0x02, 0x7f, 0x41,
+    0x00, 0x41, 0x00, 0x10, 0x04, 0x0b, 0x1a, 0x0b, 0x66, 0x01, 0x02, 0x7f,
+    0x41, 0x90, 0x08, 0x28, 0x02, 0x00, 0x22, 0x00, 0x28, 0x02, 0x4c, 0x41,
+    0x00, 0x4e, 0x04, 0x7f, 0x41, 0x01, 0x05, 0x20, 0x01, 0x0b, 0x1a, 0x02,
+    0x40, 0x41, 0x7f, 0x41, 0x00, 0x10, 0x0a, 0x22, 0x01, 0x20, 0x01, 0x20,
+    0x00, 0x10, 0x09, 0x47, 0x1b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x02, 0x40,
+    0x20, 0x00, 0x2d, 0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00,
+    0x28, 0x02, 0x14, 0x22, 0x01, 0x20, 0x00, 0x28, 0x02, 0x10, 0x4f, 0x0d,
+    0x00, 0x20, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a, 0x36, 0x02, 0x14, 0x20,
+    0x01, 0x41, 0x0a, 0x3a, 0x00, 0x00, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x10,
+    0x06, 0x0b, 0x0b, 0x3d, 0x01, 0x01, 0x7f, 0x20, 0x02, 0x04, 0x40, 0x03,
+    0x40, 0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0xc0, 0x00, 0x49, 0x1b, 0x22, 0x03, 0x10, 0x03, 0x21,
+    0x00, 0x20, 0x01, 0x41, 0x80, 0x40, 0x6b, 0x21, 0x01, 0x20, 0x00, 0x41,
+    0x80, 0x40, 0x6b, 0x21, 0x00, 0x20, 0x02, 0x20, 0x03, 0x6b, 0x22, 0x02,
+    0x0d, 0x00, 0x0b, 0x0b, 0x0b, 0xb1, 0x02, 0x01, 0x06, 0x7f, 0x23, 0x00,
+    0x41, 0x20, 0x6b, 0x22, 0x03, 0x24, 0x00, 0x20, 0x03, 0x20, 0x00, 0x28,
+    0x02, 0x1c, 0x22, 0x04, 0x36, 0x02, 0x10, 0x20, 0x00, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x03, 0x20, 0x02, 0x36, 0x02, 0x1c, 0x20, 0x03, 0x20,
+    0x01, 0x36, 0x02, 0x18, 0x20, 0x03, 0x20, 0x05, 0x20, 0x04, 0x6b, 0x22,
+    0x01, 0x36, 0x02, 0x14, 0x20, 0x01, 0x20, 0x02, 0x6a, 0x21, 0x06, 0x41,
+    0x02, 0x21, 0x05, 0x20, 0x03, 0x41, 0x10, 0x6a, 0x21, 0x01, 0x03, 0x40,
+    0x02, 0x40, 0x02, 0x7f, 0x20, 0x06, 0x02, 0x7f, 0x20, 0x00, 0x28, 0x02,
+    0x3c, 0x20, 0x01, 0x20, 0x05, 0x20, 0x03, 0x41, 0x0c, 0x6a, 0x10, 0x00,
+    0x04, 0x40, 0x20, 0x03, 0x41, 0x7f, 0x36, 0x02, 0x0c, 0x41, 0x7f, 0x0c,
+    0x01, 0x0b, 0x20, 0x03, 0x28, 0x02, 0x0c, 0x0b, 0x22, 0x04, 0x46, 0x04,
+    0x40, 0x20, 0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02,
+    0x1c, 0x20, 0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x20, 0x02, 0x0c,
+    0x01, 0x0b, 0x20, 0x04, 0x41, 0x7f, 0x4a, 0x0d, 0x01, 0x20, 0x00, 0x41,
+    0x00, 0x36, 0x02, 0x1c, 0x20, 0x00, 0x42, 0x00, 0x37, 0x03, 0x10, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x00, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x00, 0x20, 0x05, 0x41, 0x02, 0x46, 0x0d, 0x00, 0x1a, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x04, 0x6b, 0x0b, 0x21, 0x04, 0x20, 0x03, 0x41,
+    0x20, 0x6a, 0x24, 0x00, 0x20, 0x04, 0x0f, 0x0b, 0x20, 0x01, 0x41, 0x08,
+    0x6a, 0x20, 0x01, 0x20, 0x04, 0x20, 0x01, 0x28, 0x02, 0x04, 0x22, 0x07,
+    0x4b, 0x22, 0x08, 0x1b, 0x22, 0x01, 0x20, 0x04, 0x20, 0x07, 0x41, 0x00,
+    0x20, 0x08, 0x1b, 0x6b, 0x22, 0x07, 0x20, 0x01, 0x28, 0x02, 0x00, 0x6a,
+    0x36, 0x02, 0x00, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x04, 0x20, 0x07,
+    0x6b, 0x36, 0x02, 0x04, 0x20, 0x06, 0x20, 0x04, 0x6b, 0x21, 0x06, 0x20,
+    0x05, 0x20, 0x08, 0x6b, 0x21, 0x05, 0x0c, 0x00, 0x00, 0x0b, 0x00, 0x0b,
+    0x0b, 0x4d, 0x06, 0x00, 0x41, 0x80, 0x08, 0x0b, 0x12, 0x68, 0x65, 0x6c,
+    0x6c, 0x6f, 0x2c, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x21, 0x00, 0x00,
+    0x00, 0x18, 0x04, 0x00, 0x41, 0x98, 0x08, 0x0b, 0x01, 0x05, 0x00, 0x41,
+    0xa4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xbc, 0x08, 0x0b, 0x0e, 0x02,
+    0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0xb8, 0x04, 0x00, 0x00, 0x00,
+    0x04, 0x00, 0x41, 0xd4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xe3, 0x08,
+    0x0b, 0x05, 0x0a, 0xff, 0xff, 0xff, 0xff,
+  ]);
+
+  // Trying to import WASI twice.
+  Expect.throws(
+      () => WasmModule(helloWorldData).instantiate().enableWasi().enableWasi(),
+      (Exception e) => "$e".contains("WASI is already enabled"));
+
+  // Missing imports due to not enabling WASI.
+  Expect.throws(() => WasmModule(helloWorldData).instantiate().build(),
+      (Exception e) => "$e".contains("Missing import"));
+
+  // Trying to get stdout/stderr without WASI enabled (WASI function import has
+  // been manually filled).
+  var inst = WasmModule(helloWorldData)
+      .instantiate()
+      .addFunction("wasi_unstable", "fd_write",
+          (int fd, int iovs, int iovs_len, int unused) => 0)
+      .build();
+  Expect.throws(
+      () => inst.stdout,
+      (Exception e) =>
+          "$e".contains("Can't capture stdout without WASI enabled"));
+  Expect.throws(
+      () => inst.stderr,
+      (Exception e) =>
+          "$e".contains("Can't capture stderr without WASI enabled"));
+}
diff --git a/tests/lib_2/wasm/fn_import_error_test.dart b/tests/lib_2/wasm/fn_import_error_test.dart
index 844c9bfb9f9..aeca278487d 100644
--- a/tests/lib_2/wasm/fn_import_error_test.dart
+++ b/tests/lib_2/wasm/fn_import_error_test.dart
@@ -27,25 +27,42 @@ void main() {
   var mod = WasmModule(data);
 
   // Valid instantiation.
-  var inst = mod.instantiate()
-    .addFunction(
-        "env", "someFn", (int a, int b, num c, double d) => 123).build();
+  var inst = mod
+      .instantiate()
+      .addFunction("env", "someFn", (int a, int b, num c, double d) => 123)
+      .build();
 
   // Missing imports.
-  Expect.throws(() => mod.instantiate().build(), (Exception e) => "$e".contains("Missing import"));
+  Expect.throws(() => mod.instantiate().build(),
+      (Exception e) => "$e".contains("Missing import"));
 
   // Wrong kind of import.
-  Expect.throws(() => mod.instantiate().addMemory("env", "someFn", mod.createMemory(10)), (Exception e) => "$e".contains("Import is not a memory"));
+  Expect.throws(
+      () => mod.instantiate().addMemory("env", "someFn", mod.createMemory(10)),
+      (Exception e) => "$e".contains("Import is not a memory"));
 
   // Wrong namespace.
-  Expect.throws(() => mod.instantiate().addFunction("foo", "someFn", (int a, int b, num c, double d) => 123).build(), (Exception e) => "$e".contains("Import not found"));
+  Expect.throws(
+      () => mod
+          .instantiate()
+          .addFunction("foo", "someFn", (int a, int b, num c, double d) => 123)
+          .build(),
+      (Exception e) => "$e".contains("Import not found"));
 
   // Wrong name.
-  Expect.throws(() => mod.instantiate().addFunction("env", "otherFn", (int a, int b, num c, double d) => 123).build(), (Exception e) => "$e".contains("Import not found"));
+  Expect.throws(
+      () => mod
+          .instantiate()
+          .addFunction("env", "otherFn", (int a, int b, num c, double d) => 123)
+          .build(),
+      (Exception e) => "$e".contains("Import not found"));
 
   // Already filled.
-  Expect.throws(() => mod.instantiate()
-    .addFunction("env", "someFn", (int a, int b, num c, double d) => 123)
-    .addFunction("env", "someFn", (int a, int b, num c, double d) => 456)
-    .build(), (Exception e) => "$e".contains("Import already filled"));
+  Expect.throws(
+      () => mod
+          .instantiate()
+          .addFunction("env", "someFn", (int a, int b, num c, double d) => 123)
+          .addFunction("env", "someFn", (int a, int b, num c, double d) => 456)
+          .build(),
+      (Exception e) => "$e".contains("Import already filled"));
 }
diff --git a/tests/lib_2/wasm/hello_wasi_test.dart b/tests/lib_2/wasm/hello_wasi_test.dart
new file mode 100644
index 00000000000..d862b8968b1
--- /dev/null
+++ b/tests/lib_2/wasm/hello_wasi_test.dart
@@ -0,0 +1,184 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Variant of hello_world_test that uses the default WASI imports.
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+import "package:wasm/wasm.dart";
+import "dart:convert";
+import "dart:typed_data";
+
+void main() async {
+  asyncStart();
+
+  // Hello world module generated by emscripten+WASI. Exports a function like
+  // `void _start()`, and prints using `int fd_write(int, int, int, int)`.
+  var data = Uint8List.fromList([
+    0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x33, 0x09, 0x60,
+    0x03, 0x7f, 0x7f, 0x7f, 0x01, 0x7f, 0x60, 0x04, 0x7f, 0x7f, 0x7f, 0x7f,
+    0x01, 0x7f, 0x60, 0x00, 0x00, 0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x60,
+    0x01, 0x7f, 0x01, 0x7f, 0x60, 0x03, 0x7f, 0x7e, 0x7f, 0x01, 0x7e, 0x60,
+    0x00, 0x01, 0x7f, 0x60, 0x01, 0x7f, 0x00, 0x60, 0x03, 0x7f, 0x7f, 0x7f,
+    0x00, 0x02, 0x1a, 0x01, 0x0d, 0x77, 0x61, 0x73, 0x69, 0x5f, 0x75, 0x6e,
+    0x73, 0x74, 0x61, 0x62, 0x6c, 0x65, 0x08, 0x66, 0x64, 0x5f, 0x77, 0x72,
+    0x69, 0x74, 0x65, 0x00, 0x01, 0x03, 0x0f, 0x0e, 0x03, 0x04, 0x00, 0x03,
+    0x02, 0x07, 0x05, 0x04, 0x03, 0x06, 0x02, 0x02, 0x08, 0x00, 0x04, 0x05,
+    0x01, 0x70, 0x01, 0x04, 0x04, 0x05, 0x06, 0x01, 0x01, 0x80, 0x02, 0x80,
+    0x02, 0x06, 0x09, 0x01, 0x7f, 0x01, 0x41, 0xc0, 0x95, 0xc0, 0x02, 0x0b,
+    0x07, 0x2e, 0x04, 0x06, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x02, 0x00,
+    0x11, 0x5f, 0x5f, 0x77, 0x61, 0x73, 0x6d, 0x5f, 0x63, 0x61, 0x6c, 0x6c,
+    0x5f, 0x63, 0x74, 0x6f, 0x72, 0x73, 0x00, 0x05, 0x04, 0x6d, 0x61, 0x69,
+    0x6e, 0x00, 0x04, 0x06, 0x5f, 0x73, 0x74, 0x61, 0x72, 0x74, 0x00, 0x0b,
+    0x09, 0x09, 0x01, 0x00, 0x41, 0x01, 0x0b, 0x03, 0x08, 0x0e, 0x07, 0x0a,
+    0xae, 0x0c, 0x0e, 0xbf, 0x01, 0x01, 0x05, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x04, 0x02, 0x40, 0x20, 0x01, 0x28, 0x02, 0x10, 0x22, 0x02, 0x04, 0x7f,
+    0x20, 0x02, 0x05, 0x20, 0x01, 0x10, 0x02, 0x0d, 0x01, 0x20, 0x01, 0x28,
+    0x02, 0x10, 0x0b, 0x20, 0x01, 0x28, 0x02, 0x14, 0x22, 0x05, 0x6b, 0x20,
+    0x00, 0x49, 0x04, 0x40, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20, 0x00, 0x20,
+    0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x0f, 0x0b, 0x02, 0x40, 0x20,
+    0x01, 0x2c, 0x00, 0x4b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x20, 0x00, 0x21,
+    0x03, 0x03, 0x40, 0x20, 0x03, 0x22, 0x02, 0x45, 0x0d, 0x01, 0x20, 0x02,
+    0x41, 0x7f, 0x6a, 0x22, 0x03, 0x41, 0x80, 0x08, 0x6a, 0x2d, 0x00, 0x00,
+    0x41, 0x0a, 0x47, 0x0d, 0x00, 0x0b, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20,
+    0x02, 0x20, 0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x22, 0x03, 0x20,
+    0x02, 0x49, 0x0d, 0x01, 0x20, 0x00, 0x20, 0x02, 0x6b, 0x21, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0x08, 0x6a, 0x21, 0x04, 0x20, 0x01, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x02, 0x21, 0x06, 0x0b, 0x20, 0x05, 0x20, 0x04, 0x20,
+    0x00, 0x10, 0x03, 0x1a, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x14, 0x20,
+    0x00, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x06, 0x6a, 0x21, 0x03,
+    0x0b, 0x20, 0x03, 0x0b, 0x59, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x20, 0x00,
+    0x2d, 0x00, 0x4a, 0x22, 0x01, 0x41, 0x7f, 0x6a, 0x20, 0x01, 0x72, 0x3a,
+    0x00, 0x4a, 0x20, 0x00, 0x28, 0x02, 0x00, 0x22, 0x01, 0x41, 0x08, 0x71,
+    0x04, 0x40, 0x20, 0x00, 0x20, 0x01, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x7f, 0x0f, 0x0b, 0x20, 0x00, 0x42, 0x00, 0x37, 0x02, 0x04, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02, 0x1c, 0x20,
+    0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01, 0x20, 0x00,
+    0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x41, 0x00, 0x0b, 0x82, 0x04,
+    0x01, 0x03, 0x7f, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x4f, 0x04, 0x40,
+    0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x10, 0x0d, 0x20, 0x00, 0x0f, 0x0b,
+    0x20, 0x00, 0x20, 0x02, 0x6a, 0x21, 0x03, 0x02, 0x40, 0x20, 0x00, 0x20,
+    0x01, 0x73, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x02, 0x40, 0x20, 0x02,
+    0x41, 0x01, 0x48, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b,
+    0x20, 0x00, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02, 0x03, 0x40, 0x20, 0x02, 0x20,
+    0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a,
+    0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02, 0x20, 0x03, 0x4f,
+    0x0d, 0x01, 0x20, 0x02, 0x41, 0x03, 0x71, 0x0d, 0x00, 0x0b, 0x0b, 0x02,
+    0x40, 0x20, 0x03, 0x41, 0x7c, 0x71, 0x22, 0x04, 0x41, 0xc0, 0x00, 0x49,
+    0x0d, 0x00, 0x20, 0x02, 0x20, 0x04, 0x41, 0x40, 0x6a, 0x22, 0x05, 0x4b,
+    0x0d, 0x00, 0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36,
+    0x02, 0x00, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x04, 0x36, 0x02, 0x04,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x08, 0x36, 0x02, 0x08, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x0c, 0x36, 0x02, 0x0c, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x10, 0x36, 0x02, 0x10, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x14, 0x36, 0x02, 0x14, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x18, 0x36,
+    0x02, 0x18, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x1c, 0x36, 0x02, 0x1c,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x20, 0x36, 0x02, 0x20, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x24, 0x36, 0x02, 0x24, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x28, 0x36, 0x02, 0x28, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x2c, 0x36, 0x02, 0x2c, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x30, 0x36,
+    0x02, 0x30, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x34, 0x36, 0x02, 0x34,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x38, 0x36, 0x02, 0x38, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x3c, 0x36, 0x02, 0x3c, 0x20, 0x01, 0x41, 0x40,
+    0x6b, 0x21, 0x01, 0x20, 0x02, 0x41, 0x40, 0x6b, 0x22, 0x02, 0x20, 0x05,
+    0x4d, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x04, 0x4f, 0x0d, 0x01,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36, 0x02, 0x00,
+    0x20, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x04, 0x6a,
+    0x22, 0x02, 0x20, 0x04, 0x49, 0x0d, 0x00, 0x0b, 0x0c, 0x01, 0x0b, 0x20,
+    0x03, 0x41, 0x04, 0x49, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01,
+    0x0b, 0x20, 0x03, 0x41, 0x7c, 0x6a, 0x22, 0x04, 0x20, 0x00, 0x49, 0x04,
+    0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x3a, 0x00, 0x01, 0x20, 0x02,
+    0x20, 0x01, 0x2d, 0x00, 0x02, 0x3a, 0x00, 0x02, 0x20, 0x02, 0x20, 0x01,
+    0x2d, 0x00, 0x03, 0x3a, 0x00, 0x03, 0x20, 0x01, 0x41, 0x04, 0x6a, 0x21,
+    0x01, 0x20, 0x02, 0x41, 0x04, 0x6a, 0x22, 0x02, 0x20, 0x04, 0x4d, 0x0d,
+    0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x03, 0x49, 0x04, 0x40, 0x03, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01,
+    0x41, 0x01, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02,
+    0x20, 0x03, 0x47, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x00, 0x0b, 0x06, 0x00,
+    0x10, 0x0c, 0x41, 0x00, 0x0b, 0x03, 0x00, 0x01, 0x0b, 0x7e, 0x01, 0x03,
+    0x7f, 0x23, 0x00, 0x41, 0x10, 0x6b, 0x22, 0x01, 0x24, 0x00, 0x20, 0x01,
+    0x41, 0x0a, 0x3a, 0x00, 0x0f, 0x02, 0x40, 0x20, 0x00, 0x28, 0x02, 0x10,
+    0x22, 0x02, 0x45, 0x04, 0x40, 0x20, 0x00, 0x10, 0x02, 0x0d, 0x01, 0x20,
+    0x00, 0x28, 0x02, 0x10, 0x21, 0x02, 0x0b, 0x02, 0x40, 0x20, 0x00, 0x28,
+    0x02, 0x14, 0x22, 0x03, 0x20, 0x02, 0x4f, 0x0d, 0x00, 0x20, 0x00, 0x2c,
+    0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00, 0x20, 0x03, 0x41,
+    0x01, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x03, 0x41, 0x0a, 0x3a, 0x00, 0x00,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x20, 0x01, 0x41, 0x0f, 0x6a, 0x41, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x41, 0x01, 0x47, 0x0d,
+    0x00, 0x20, 0x01, 0x2d, 0x00, 0x0f, 0x1a, 0x0b, 0x20, 0x01, 0x41, 0x10,
+    0x6a, 0x24, 0x00, 0x0b, 0x04, 0x00, 0x42, 0x00, 0x0b, 0x04, 0x00, 0x41,
+    0x00, 0x0b, 0x31, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x21, 0x02, 0x20, 0x02,
+    0x02, 0x7f, 0x20, 0x01, 0x28, 0x02, 0x4c, 0x41, 0x7f, 0x4c, 0x04, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x10, 0x01, 0x0c, 0x01, 0x0b, 0x20, 0x02, 0x20,
+    0x01, 0x10, 0x01, 0x0b, 0x22, 0x01, 0x46, 0x04, 0x40, 0x20, 0x00, 0x0f,
+    0x0b, 0x20, 0x01, 0x0b, 0x62, 0x01, 0x03, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x00, 0x03, 0x40, 0x20, 0x00, 0x22, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x00,
+    0x20, 0x01, 0x28, 0x02, 0x00, 0x22, 0x02, 0x41, 0x7f, 0x73, 0x20, 0x02,
+    0x41, 0xff, 0xfd, 0xfb, 0x77, 0x6a, 0x71, 0x41, 0x80, 0x81, 0x82, 0x84,
+    0x78, 0x71, 0x45, 0x0d, 0x00, 0x0b, 0x02, 0x40, 0x20, 0x02, 0x41, 0xff,
+    0x01, 0x71, 0x45, 0x04, 0x40, 0x20, 0x01, 0x21, 0x00, 0x0c, 0x01, 0x0b,
+    0x03, 0x40, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x21, 0x02, 0x20, 0x01, 0x41,
+    0x01, 0x6a, 0x22, 0x00, 0x21, 0x01, 0x20, 0x02, 0x0d, 0x00, 0x0b, 0x0b,
+    0x20, 0x00, 0x41, 0x80, 0x08, 0x6b, 0x0b, 0x0c, 0x00, 0x02, 0x7f, 0x41,
+    0x00, 0x41, 0x00, 0x10, 0x04, 0x0b, 0x1a, 0x0b, 0x66, 0x01, 0x02, 0x7f,
+    0x41, 0x90, 0x08, 0x28, 0x02, 0x00, 0x22, 0x00, 0x28, 0x02, 0x4c, 0x41,
+    0x00, 0x4e, 0x04, 0x7f, 0x41, 0x01, 0x05, 0x20, 0x01, 0x0b, 0x1a, 0x02,
+    0x40, 0x41, 0x7f, 0x41, 0x00, 0x10, 0x0a, 0x22, 0x01, 0x20, 0x01, 0x20,
+    0x00, 0x10, 0x09, 0x47, 0x1b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x02, 0x40,
+    0x20, 0x00, 0x2d, 0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00,
+    0x28, 0x02, 0x14, 0x22, 0x01, 0x20, 0x00, 0x28, 0x02, 0x10, 0x4f, 0x0d,
+    0x00, 0x20, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a, 0x36, 0x02, 0x14, 0x20,
+    0x01, 0x41, 0x0a, 0x3a, 0x00, 0x00, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x10,
+    0x06, 0x0b, 0x0b, 0x3d, 0x01, 0x01, 0x7f, 0x20, 0x02, 0x04, 0x40, 0x03,
+    0x40, 0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0xc0, 0x00, 0x49, 0x1b, 0x22, 0x03, 0x10, 0x03, 0x21,
+    0x00, 0x20, 0x01, 0x41, 0x80, 0x40, 0x6b, 0x21, 0x01, 0x20, 0x00, 0x41,
+    0x80, 0x40, 0x6b, 0x21, 0x00, 0x20, 0x02, 0x20, 0x03, 0x6b, 0x22, 0x02,
+    0x0d, 0x00, 0x0b, 0x0b, 0x0b, 0xb1, 0x02, 0x01, 0x06, 0x7f, 0x23, 0x00,
+    0x41, 0x20, 0x6b, 0x22, 0x03, 0x24, 0x00, 0x20, 0x03, 0x20, 0x00, 0x28,
+    0x02, 0x1c, 0x22, 0x04, 0x36, 0x02, 0x10, 0x20, 0x00, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x03, 0x20, 0x02, 0x36, 0x02, 0x1c, 0x20, 0x03, 0x20,
+    0x01, 0x36, 0x02, 0x18, 0x20, 0x03, 0x20, 0x05, 0x20, 0x04, 0x6b, 0x22,
+    0x01, 0x36, 0x02, 0x14, 0x20, 0x01, 0x20, 0x02, 0x6a, 0x21, 0x06, 0x41,
+    0x02, 0x21, 0x05, 0x20, 0x03, 0x41, 0x10, 0x6a, 0x21, 0x01, 0x03, 0x40,
+    0x02, 0x40, 0x02, 0x7f, 0x20, 0x06, 0x02, 0x7f, 0x20, 0x00, 0x28, 0x02,
+    0x3c, 0x20, 0x01, 0x20, 0x05, 0x20, 0x03, 0x41, 0x0c, 0x6a, 0x10, 0x00,
+    0x04, 0x40, 0x20, 0x03, 0x41, 0x7f, 0x36, 0x02, 0x0c, 0x41, 0x7f, 0x0c,
+    0x01, 0x0b, 0x20, 0x03, 0x28, 0x02, 0x0c, 0x0b, 0x22, 0x04, 0x46, 0x04,
+    0x40, 0x20, 0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02,
+    0x1c, 0x20, 0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x20, 0x02, 0x0c,
+    0x01, 0x0b, 0x20, 0x04, 0x41, 0x7f, 0x4a, 0x0d, 0x01, 0x20, 0x00, 0x41,
+    0x00, 0x36, 0x02, 0x1c, 0x20, 0x00, 0x42, 0x00, 0x37, 0x03, 0x10, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x00, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x00, 0x20, 0x05, 0x41, 0x02, 0x46, 0x0d, 0x00, 0x1a, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x04, 0x6b, 0x0b, 0x21, 0x04, 0x20, 0x03, 0x41,
+    0x20, 0x6a, 0x24, 0x00, 0x20, 0x04, 0x0f, 0x0b, 0x20, 0x01, 0x41, 0x08,
+    0x6a, 0x20, 0x01, 0x20, 0x04, 0x20, 0x01, 0x28, 0x02, 0x04, 0x22, 0x07,
+    0x4b, 0x22, 0x08, 0x1b, 0x22, 0x01, 0x20, 0x04, 0x20, 0x07, 0x41, 0x00,
+    0x20, 0x08, 0x1b, 0x6b, 0x22, 0x07, 0x20, 0x01, 0x28, 0x02, 0x00, 0x6a,
+    0x36, 0x02, 0x00, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x04, 0x20, 0x07,
+    0x6b, 0x36, 0x02, 0x04, 0x20, 0x06, 0x20, 0x04, 0x6b, 0x21, 0x06, 0x20,
+    0x05, 0x20, 0x08, 0x6b, 0x21, 0x05, 0x0c, 0x00, 0x00, 0x0b, 0x00, 0x0b,
+    0x0b, 0x4d, 0x06, 0x00, 0x41, 0x80, 0x08, 0x0b, 0x12, 0x68, 0x65, 0x6c,
+    0x6c, 0x6f, 0x2c, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x21, 0x00, 0x00,
+    0x00, 0x18, 0x04, 0x00, 0x41, 0x98, 0x08, 0x0b, 0x01, 0x05, 0x00, 0x41,
+    0xa4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xbc, 0x08, 0x0b, 0x0e, 0x02,
+    0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0xb8, 0x04, 0x00, 0x00, 0x00,
+    0x04, 0x00, 0x41, 0xd4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xe3, 0x08,
+    0x0b, 0x05, 0x0a, 0xff, 0xff, 0xff, 0xff,
+  ]);
+
+  var inst =
+      WasmModule(data).instantiate().enableWasi(captureStdout: true).build();
+
+  var fn = inst.lookupFunction("_start");
+  fn();
+  var out = utf8.decode(await inst.stdout.first);
+  Expect.equals("hello, world!\n", out);
+  asyncEnd();
+}
diff --git a/tests/lib_2/wasm/wasi_error_test.dart b/tests/lib_2/wasm/wasi_error_test.dart
new file mode 100644
index 00000000000..8418dad832a
--- /dev/null
+++ b/tests/lib_2/wasm/wasi_error_test.dart
@@ -0,0 +1,204 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test the errors that can be thrown by WASI.
+
+import "package:expect/expect.dart";
+import "package:wasm/wasm.dart";
+import "dart:typed_data";
+
+void main() {
+  // Empty wasm module.
+  var emptyModuleData = Uint8List.fromList(
+      [0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x06, 0x81, 0x00, 0x00]);
+
+  // Failed to fill WASI imports (the empty module was not built with WASI).
+  Expect.throws(() => WasmModule(emptyModuleData).instantiate().enableWasi(),
+      (Exception e) => "$e".contains("Failed to fill WASI imports"));
+
+  // Hello world module generated by emscripten+WASI. Exports a function like
+  // `void _start()`, and prints using `int fd_write(int, int, int, int)`.
+  var helloWorldData = Uint8List.fromList([
+    0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x33, 0x09, 0x60,
+    0x03, 0x7f, 0x7f, 0x7f, 0x01, 0x7f, 0x60, 0x04, 0x7f, 0x7f, 0x7f, 0x7f,
+    0x01, 0x7f, 0x60, 0x00, 0x00, 0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x60,
+    0x01, 0x7f, 0x01, 0x7f, 0x60, 0x03, 0x7f, 0x7e, 0x7f, 0x01, 0x7e, 0x60,
+    0x00, 0x01, 0x7f, 0x60, 0x01, 0x7f, 0x00, 0x60, 0x03, 0x7f, 0x7f, 0x7f,
+    0x00, 0x02, 0x1a, 0x01, 0x0d, 0x77, 0x61, 0x73, 0x69, 0x5f, 0x75, 0x6e,
+    0x73, 0x74, 0x61, 0x62, 0x6c, 0x65, 0x08, 0x66, 0x64, 0x5f, 0x77, 0x72,
+    0x69, 0x74, 0x65, 0x00, 0x01, 0x03, 0x0f, 0x0e, 0x03, 0x04, 0x00, 0x03,
+    0x02, 0x07, 0x05, 0x04, 0x03, 0x06, 0x02, 0x02, 0x08, 0x00, 0x04, 0x05,
+    0x01, 0x70, 0x01, 0x04, 0x04, 0x05, 0x06, 0x01, 0x01, 0x80, 0x02, 0x80,
+    0x02, 0x06, 0x09, 0x01, 0x7f, 0x01, 0x41, 0xc0, 0x95, 0xc0, 0x02, 0x0b,
+    0x07, 0x2e, 0x04, 0x06, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x02, 0x00,
+    0x11, 0x5f, 0x5f, 0x77, 0x61, 0x73, 0x6d, 0x5f, 0x63, 0x61, 0x6c, 0x6c,
+    0x5f, 0x63, 0x74, 0x6f, 0x72, 0x73, 0x00, 0x05, 0x04, 0x6d, 0x61, 0x69,
+    0x6e, 0x00, 0x04, 0x06, 0x5f, 0x73, 0x74, 0x61, 0x72, 0x74, 0x00, 0x0b,
+    0x09, 0x09, 0x01, 0x00, 0x41, 0x01, 0x0b, 0x03, 0x08, 0x0e, 0x07, 0x0a,
+    0xae, 0x0c, 0x0e, 0xbf, 0x01, 0x01, 0x05, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x04, 0x02, 0x40, 0x20, 0x01, 0x28, 0x02, 0x10, 0x22, 0x02, 0x04, 0x7f,
+    0x20, 0x02, 0x05, 0x20, 0x01, 0x10, 0x02, 0x0d, 0x01, 0x20, 0x01, 0x28,
+    0x02, 0x10, 0x0b, 0x20, 0x01, 0x28, 0x02, 0x14, 0x22, 0x05, 0x6b, 0x20,
+    0x00, 0x49, 0x04, 0x40, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20, 0x00, 0x20,
+    0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x0f, 0x0b, 0x02, 0x40, 0x20,
+    0x01, 0x2c, 0x00, 0x4b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x20, 0x00, 0x21,
+    0x03, 0x03, 0x40, 0x20, 0x03, 0x22, 0x02, 0x45, 0x0d, 0x01, 0x20, 0x02,
+    0x41, 0x7f, 0x6a, 0x22, 0x03, 0x41, 0x80, 0x08, 0x6a, 0x2d, 0x00, 0x00,
+    0x41, 0x0a, 0x47, 0x0d, 0x00, 0x0b, 0x20, 0x01, 0x41, 0x80, 0x08, 0x20,
+    0x02, 0x20, 0x01, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x22, 0x03, 0x20,
+    0x02, 0x49, 0x0d, 0x01, 0x20, 0x00, 0x20, 0x02, 0x6b, 0x21, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0x08, 0x6a, 0x21, 0x04, 0x20, 0x01, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x02, 0x21, 0x06, 0x0b, 0x20, 0x05, 0x20, 0x04, 0x20,
+    0x00, 0x10, 0x03, 0x1a, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x14, 0x20,
+    0x00, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x06, 0x6a, 0x21, 0x03,
+    0x0b, 0x20, 0x03, 0x0b, 0x59, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x20, 0x00,
+    0x2d, 0x00, 0x4a, 0x22, 0x01, 0x41, 0x7f, 0x6a, 0x20, 0x01, 0x72, 0x3a,
+    0x00, 0x4a, 0x20, 0x00, 0x28, 0x02, 0x00, 0x22, 0x01, 0x41, 0x08, 0x71,
+    0x04, 0x40, 0x20, 0x00, 0x20, 0x01, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x7f, 0x0f, 0x0b, 0x20, 0x00, 0x42, 0x00, 0x37, 0x02, 0x04, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02, 0x1c, 0x20,
+    0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01, 0x20, 0x00,
+    0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x41, 0x00, 0x0b, 0x82, 0x04,
+    0x01, 0x03, 0x7f, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x4f, 0x04, 0x40,
+    0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x10, 0x0d, 0x20, 0x00, 0x0f, 0x0b,
+    0x20, 0x00, 0x20, 0x02, 0x6a, 0x21, 0x03, 0x02, 0x40, 0x20, 0x00, 0x20,
+    0x01, 0x73, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x02, 0x40, 0x20, 0x02,
+    0x41, 0x01, 0x48, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b,
+    0x20, 0x00, 0x41, 0x03, 0x71, 0x45, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02, 0x03, 0x40, 0x20, 0x02, 0x20,
+    0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a,
+    0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02, 0x20, 0x03, 0x4f,
+    0x0d, 0x01, 0x20, 0x02, 0x41, 0x03, 0x71, 0x0d, 0x00, 0x0b, 0x0b, 0x02,
+    0x40, 0x20, 0x03, 0x41, 0x7c, 0x71, 0x22, 0x04, 0x41, 0xc0, 0x00, 0x49,
+    0x0d, 0x00, 0x20, 0x02, 0x20, 0x04, 0x41, 0x40, 0x6a, 0x22, 0x05, 0x4b,
+    0x0d, 0x00, 0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36,
+    0x02, 0x00, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x04, 0x36, 0x02, 0x04,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x08, 0x36, 0x02, 0x08, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x0c, 0x36, 0x02, 0x0c, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x10, 0x36, 0x02, 0x10, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x14, 0x36, 0x02, 0x14, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x18, 0x36,
+    0x02, 0x18, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x1c, 0x36, 0x02, 0x1c,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x20, 0x36, 0x02, 0x20, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x24, 0x36, 0x02, 0x24, 0x20, 0x02, 0x20, 0x01,
+    0x28, 0x02, 0x28, 0x36, 0x02, 0x28, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02,
+    0x2c, 0x36, 0x02, 0x2c, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x30, 0x36,
+    0x02, 0x30, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x34, 0x36, 0x02, 0x34,
+    0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x38, 0x36, 0x02, 0x38, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x3c, 0x36, 0x02, 0x3c, 0x20, 0x01, 0x41, 0x40,
+    0x6b, 0x21, 0x01, 0x20, 0x02, 0x41, 0x40, 0x6b, 0x22, 0x02, 0x20, 0x05,
+    0x4d, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x04, 0x4f, 0x0d, 0x01,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x28, 0x02, 0x00, 0x36, 0x02, 0x00,
+    0x20, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x04, 0x6a,
+    0x22, 0x02, 0x20, 0x04, 0x49, 0x0d, 0x00, 0x0b, 0x0c, 0x01, 0x0b, 0x20,
+    0x03, 0x41, 0x04, 0x49, 0x04, 0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01,
+    0x0b, 0x20, 0x03, 0x41, 0x7c, 0x6a, 0x22, 0x04, 0x20, 0x00, 0x49, 0x04,
+    0x40, 0x20, 0x00, 0x21, 0x02, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x21, 0x02,
+    0x03, 0x40, 0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x3a, 0x00, 0x01, 0x20, 0x02,
+    0x20, 0x01, 0x2d, 0x00, 0x02, 0x3a, 0x00, 0x02, 0x20, 0x02, 0x20, 0x01,
+    0x2d, 0x00, 0x03, 0x3a, 0x00, 0x03, 0x20, 0x01, 0x41, 0x04, 0x6a, 0x21,
+    0x01, 0x20, 0x02, 0x41, 0x04, 0x6a, 0x22, 0x02, 0x20, 0x04, 0x4d, 0x0d,
+    0x00, 0x0b, 0x0b, 0x20, 0x02, 0x20, 0x03, 0x49, 0x04, 0x40, 0x03, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x2d, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x20, 0x01,
+    0x41, 0x01, 0x6a, 0x21, 0x01, 0x20, 0x02, 0x41, 0x01, 0x6a, 0x22, 0x02,
+    0x20, 0x03, 0x47, 0x0d, 0x00, 0x0b, 0x0b, 0x20, 0x00, 0x0b, 0x06, 0x00,
+    0x10, 0x0c, 0x41, 0x00, 0x0b, 0x03, 0x00, 0x01, 0x0b, 0x7e, 0x01, 0x03,
+    0x7f, 0x23, 0x00, 0x41, 0x10, 0x6b, 0x22, 0x01, 0x24, 0x00, 0x20, 0x01,
+    0x41, 0x0a, 0x3a, 0x00, 0x0f, 0x02, 0x40, 0x20, 0x00, 0x28, 0x02, 0x10,
+    0x22, 0x02, 0x45, 0x04, 0x40, 0x20, 0x00, 0x10, 0x02, 0x0d, 0x01, 0x20,
+    0x00, 0x28, 0x02, 0x10, 0x21, 0x02, 0x0b, 0x02, 0x40, 0x20, 0x00, 0x28,
+    0x02, 0x14, 0x22, 0x03, 0x20, 0x02, 0x4f, 0x0d, 0x00, 0x20, 0x00, 0x2c,
+    0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00, 0x20, 0x03, 0x41,
+    0x01, 0x6a, 0x36, 0x02, 0x14, 0x20, 0x03, 0x41, 0x0a, 0x3a, 0x00, 0x00,
+    0x0c, 0x01, 0x0b, 0x20, 0x00, 0x20, 0x01, 0x41, 0x0f, 0x6a, 0x41, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x24, 0x11, 0x00, 0x00, 0x41, 0x01, 0x47, 0x0d,
+    0x00, 0x20, 0x01, 0x2d, 0x00, 0x0f, 0x1a, 0x0b, 0x20, 0x01, 0x41, 0x10,
+    0x6a, 0x24, 0x00, 0x0b, 0x04, 0x00, 0x42, 0x00, 0x0b, 0x04, 0x00, 0x41,
+    0x00, 0x0b, 0x31, 0x01, 0x01, 0x7f, 0x20, 0x00, 0x21, 0x02, 0x20, 0x02,
+    0x02, 0x7f, 0x20, 0x01, 0x28, 0x02, 0x4c, 0x41, 0x7f, 0x4c, 0x04, 0x40,
+    0x20, 0x02, 0x20, 0x01, 0x10, 0x01, 0x0c, 0x01, 0x0b, 0x20, 0x02, 0x20,
+    0x01, 0x10, 0x01, 0x0b, 0x22, 0x01, 0x46, 0x04, 0x40, 0x20, 0x00, 0x0f,
+    0x0b, 0x20, 0x01, 0x0b, 0x62, 0x01, 0x03, 0x7f, 0x41, 0x80, 0x08, 0x21,
+    0x00, 0x03, 0x40, 0x20, 0x00, 0x22, 0x01, 0x41, 0x04, 0x6a, 0x21, 0x00,
+    0x20, 0x01, 0x28, 0x02, 0x00, 0x22, 0x02, 0x41, 0x7f, 0x73, 0x20, 0x02,
+    0x41, 0xff, 0xfd, 0xfb, 0x77, 0x6a, 0x71, 0x41, 0x80, 0x81, 0x82, 0x84,
+    0x78, 0x71, 0x45, 0x0d, 0x00, 0x0b, 0x02, 0x40, 0x20, 0x02, 0x41, 0xff,
+    0x01, 0x71, 0x45, 0x04, 0x40, 0x20, 0x01, 0x21, 0x00, 0x0c, 0x01, 0x0b,
+    0x03, 0x40, 0x20, 0x01, 0x2d, 0x00, 0x01, 0x21, 0x02, 0x20, 0x01, 0x41,
+    0x01, 0x6a, 0x22, 0x00, 0x21, 0x01, 0x20, 0x02, 0x0d, 0x00, 0x0b, 0x0b,
+    0x20, 0x00, 0x41, 0x80, 0x08, 0x6b, 0x0b, 0x0c, 0x00, 0x02, 0x7f, 0x41,
+    0x00, 0x41, 0x00, 0x10, 0x04, 0x0b, 0x1a, 0x0b, 0x66, 0x01, 0x02, 0x7f,
+    0x41, 0x90, 0x08, 0x28, 0x02, 0x00, 0x22, 0x00, 0x28, 0x02, 0x4c, 0x41,
+    0x00, 0x4e, 0x04, 0x7f, 0x41, 0x01, 0x05, 0x20, 0x01, 0x0b, 0x1a, 0x02,
+    0x40, 0x41, 0x7f, 0x41, 0x00, 0x10, 0x0a, 0x22, 0x01, 0x20, 0x01, 0x20,
+    0x00, 0x10, 0x09, 0x47, 0x1b, 0x41, 0x00, 0x48, 0x0d, 0x00, 0x02, 0x40,
+    0x20, 0x00, 0x2d, 0x00, 0x4b, 0x41, 0x0a, 0x46, 0x0d, 0x00, 0x20, 0x00,
+    0x28, 0x02, 0x14, 0x22, 0x01, 0x20, 0x00, 0x28, 0x02, 0x10, 0x4f, 0x0d,
+    0x00, 0x20, 0x00, 0x20, 0x01, 0x41, 0x01, 0x6a, 0x36, 0x02, 0x14, 0x20,
+    0x01, 0x41, 0x0a, 0x3a, 0x00, 0x00, 0x0c, 0x01, 0x0b, 0x20, 0x00, 0x10,
+    0x06, 0x0b, 0x0b, 0x3d, 0x01, 0x01, 0x7f, 0x20, 0x02, 0x04, 0x40, 0x03,
+    0x40, 0x20, 0x00, 0x20, 0x01, 0x20, 0x02, 0x41, 0x80, 0xc0, 0x00, 0x20,
+    0x02, 0x41, 0x80, 0xc0, 0x00, 0x49, 0x1b, 0x22, 0x03, 0x10, 0x03, 0x21,
+    0x00, 0x20, 0x01, 0x41, 0x80, 0x40, 0x6b, 0x21, 0x01, 0x20, 0x00, 0x41,
+    0x80, 0x40, 0x6b, 0x21, 0x00, 0x20, 0x02, 0x20, 0x03, 0x6b, 0x22, 0x02,
+    0x0d, 0x00, 0x0b, 0x0b, 0x0b, 0xb1, 0x02, 0x01, 0x06, 0x7f, 0x23, 0x00,
+    0x41, 0x20, 0x6b, 0x22, 0x03, 0x24, 0x00, 0x20, 0x03, 0x20, 0x00, 0x28,
+    0x02, 0x1c, 0x22, 0x04, 0x36, 0x02, 0x10, 0x20, 0x00, 0x28, 0x02, 0x14,
+    0x21, 0x05, 0x20, 0x03, 0x20, 0x02, 0x36, 0x02, 0x1c, 0x20, 0x03, 0x20,
+    0x01, 0x36, 0x02, 0x18, 0x20, 0x03, 0x20, 0x05, 0x20, 0x04, 0x6b, 0x22,
+    0x01, 0x36, 0x02, 0x14, 0x20, 0x01, 0x20, 0x02, 0x6a, 0x21, 0x06, 0x41,
+    0x02, 0x21, 0x05, 0x20, 0x03, 0x41, 0x10, 0x6a, 0x21, 0x01, 0x03, 0x40,
+    0x02, 0x40, 0x02, 0x7f, 0x20, 0x06, 0x02, 0x7f, 0x20, 0x00, 0x28, 0x02,
+    0x3c, 0x20, 0x01, 0x20, 0x05, 0x20, 0x03, 0x41, 0x0c, 0x6a, 0x10, 0x00,
+    0x04, 0x40, 0x20, 0x03, 0x41, 0x7f, 0x36, 0x02, 0x0c, 0x41, 0x7f, 0x0c,
+    0x01, 0x0b, 0x20, 0x03, 0x28, 0x02, 0x0c, 0x0b, 0x22, 0x04, 0x46, 0x04,
+    0x40, 0x20, 0x00, 0x20, 0x00, 0x28, 0x02, 0x2c, 0x22, 0x01, 0x36, 0x02,
+    0x1c, 0x20, 0x00, 0x20, 0x01, 0x36, 0x02, 0x14, 0x20, 0x00, 0x20, 0x01,
+    0x20, 0x00, 0x28, 0x02, 0x30, 0x6a, 0x36, 0x02, 0x10, 0x20, 0x02, 0x0c,
+    0x01, 0x0b, 0x20, 0x04, 0x41, 0x7f, 0x4a, 0x0d, 0x01, 0x20, 0x00, 0x41,
+    0x00, 0x36, 0x02, 0x1c, 0x20, 0x00, 0x42, 0x00, 0x37, 0x03, 0x10, 0x20,
+    0x00, 0x20, 0x00, 0x28, 0x02, 0x00, 0x41, 0x20, 0x72, 0x36, 0x02, 0x00,
+    0x41, 0x00, 0x20, 0x05, 0x41, 0x02, 0x46, 0x0d, 0x00, 0x1a, 0x20, 0x02,
+    0x20, 0x01, 0x28, 0x02, 0x04, 0x6b, 0x0b, 0x21, 0x04, 0x20, 0x03, 0x41,
+    0x20, 0x6a, 0x24, 0x00, 0x20, 0x04, 0x0f, 0x0b, 0x20, 0x01, 0x41, 0x08,
+    0x6a, 0x20, 0x01, 0x20, 0x04, 0x20, 0x01, 0x28, 0x02, 0x04, 0x22, 0x07,
+    0x4b, 0x22, 0x08, 0x1b, 0x22, 0x01, 0x20, 0x04, 0x20, 0x07, 0x41, 0x00,
+    0x20, 0x08, 0x1b, 0x6b, 0x22, 0x07, 0x20, 0x01, 0x28, 0x02, 0x00, 0x6a,
+    0x36, 0x02, 0x00, 0x20, 0x01, 0x20, 0x01, 0x28, 0x02, 0x04, 0x20, 0x07,
+    0x6b, 0x36, 0x02, 0x04, 0x20, 0x06, 0x20, 0x04, 0x6b, 0x21, 0x06, 0x20,
+    0x05, 0x20, 0x08, 0x6b, 0x21, 0x05, 0x0c, 0x00, 0x00, 0x0b, 0x00, 0x0b,
+    0x0b, 0x4d, 0x06, 0x00, 0x41, 0x80, 0x08, 0x0b, 0x12, 0x68, 0x65, 0x6c,
+    0x6c, 0x6f, 0x2c, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x21, 0x00, 0x00,
+    0x00, 0x18, 0x04, 0x00, 0x41, 0x98, 0x08, 0x0b, 0x01, 0x05, 0x00, 0x41,
+    0xa4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xbc, 0x08, 0x0b, 0x0e, 0x02,
+    0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0xb8, 0x04, 0x00, 0x00, 0x00,
+    0x04, 0x00, 0x41, 0xd4, 0x08, 0x0b, 0x01, 0x01, 0x00, 0x41, 0xe3, 0x08,
+    0x0b, 0x05, 0x0a, 0xff, 0xff, 0xff, 0xff,
+  ]);
+
+  // Trying to import WASI twice.
+  Expect.throws(
+      () => WasmModule(helloWorldData).instantiate().enableWasi().enableWasi(),
+      (Exception e) => "$e".contains("WASI is already enabled"));
+
+  // Missing imports due to not enabling WASI.
+  Expect.throws(() => WasmModule(helloWorldData).instantiate().build(),
+      (Exception e) => "$e".contains("Missing import"));
+
+  // Trying to get stdout/stderr without WASI enabled (WASI function import has
+  // been manually filled).
+  var inst = WasmModule(helloWorldData)
+      .instantiate()
+      .addFunction("wasi_unstable", "fd_write",
+          (int fd, int iovs, int iovs_len, int unused) => 0)
+      .build();
+  Expect.throws(
+      () => inst.stdout,
+      (Exception e) =>
+          "$e".contains("Can't capture stdout without WASI enabled"));
+  Expect.throws(
+      () => inst.stderr,
+      (Exception e) =>
+          "$e".contains("Can't capture stderr without WASI enabled"));
+}