diff --git a/pkg/dart2wasm/lib/compile.dart b/pkg/dart2wasm/lib/compile.dart
index abeeedc1452..0b4456e9db9 100644
--- a/pkg/dart2wasm/lib/compile.dart
+++ b/pkg/dart2wasm/lib/compile.dart
@@ -40,6 +40,7 @@ import 'compiler_options.dart' as compiler;
 import 'constant_evaluator.dart';
 import 'deferred_loading.dart';
 import 'dry_run.dart';
+import 'generate_wasm.dart';
 import 'io_util.dart';
 import 'js/runtime_generator.dart' as js;
 import 'modules.dart';
@@ -666,7 +667,7 @@ Future<CompilationResult> _runCodegenPhase(
   final wasmOutputFilename = path.basename(options.outputFile);
   final moduleIds = modules.keys
       .map<int>(
-        (moduleMetadata) => options.idForModuleName(
+        (moduleMetadata) => WasmCompilerOptions.idForModuleName(
           wasmOutputFilename,
           moduleMetadata.moduleName,
         )!,
diff --git a/pkg/dart2wasm/lib/compiler_options.dart b/pkg/dart2wasm/lib/compiler_options.dart
index 9642d0d77e3..e92c61a0044 100644
--- a/pkg/dart2wasm/lib/compiler_options.dart
+++ b/pkg/dart2wasm/lib/compiler_options.dart
@@ -75,12 +75,19 @@ class WasmCompilerOptions {
       translatorOptions.enableDeferredLoading ||
       translatorOptions.enableMultiModuleStressTestMode;
 
-  String moduleNameForId(String filePath, int id, {bool emitAsMain = false}) =>
-      emitAsMain || id == mainModuleId
-      ? path.basename(filePath)
-      : path.basename(path.setExtension(filePath, '_module$id.wasm'));
+  static String moduleNameForId(
+    String filePath,
+    int id, {
+    bool emitAsMain = false,
+  }) {
+    final basename = path.basename(filePath);
+    if (emitAsMain || id == mainModuleId) {
+      return basename;
+    }
+    return '${deferredModuleFilenamePrefix(basename)}$id.wasm';
+  }
 
-  int? idForModuleName(String mainWasmFilename, String moduleFilename) {
+  static int? idForModuleName(String mainWasmFilename, String moduleFilename) {
     assert(
       mainWasmFilename.endsWith('.wasm') &&
           !mainWasmFilename.contains(path.separator),
@@ -93,14 +100,28 @@ class WasmCompilerOptions {
         !moduleFilename.endsWith('.wasm')) {
       return null;
     }
-    return int.tryParse(
-      moduleFilename.substring(
-        prefix.length,
-        moduleFilename.length - '.wasm'.length,
-      ),
+    return idFromDeferredModuleFilename(moduleFilename);
+  }
+
+  /// Given a deferred module filename returns the module id.
+  ///
+  /// (i.e. returns `<id>` for `test_module<id>.wasm`).
+  static int idFromDeferredModuleFilename(String moduleName) {
+    // The name has pattern: "..._module<moduleId>.wasm"
+    assert(moduleName.endsWith('.wasm') && moduleName.contains('_module'));
+    final offset = moduleName.lastIndexOf('_module') + '_module'.length;
+    return int.parse(
+      moduleName.substring(offset, moduleName.length - '.wasm'.length),
     );
   }
 
+  /// The prefix of all deferred module filenames.
+  ///
+  /// (i.e. returns `test_module` for main module `test.wasm` and
+  /// deferred modules `test_module<id>.wasm`).
+  static String deferredModuleFilenamePrefix(String mainModuleFilename) =>
+      path.basename(path.setExtension(mainModuleFilename, '_module'));
+
   static int _defaultMaxActiveWasmOptProcesses() {
     try {
       return Platform.numberOfProcessors;
diff --git a/pkg/dart2wasm/lib/io_util.dart b/pkg/dart2wasm/lib/io_util.dart
index 9f470382102..5209fc19e7e 100644
--- a/pkg/dart2wasm/lib/io_util.dart
+++ b/pkg/dart2wasm/lib/io_util.dart
@@ -135,9 +135,12 @@ class CompilerPhaseInputOutputManager {
     int moduleId,
     List<String> flags,
   ) async {
-    final inputModuleName = options.moduleNameForId(mainWasmModule, moduleId);
+    final inputModuleName = WasmCompilerOptions.moduleNameForId(
+      mainWasmModule,
+      moduleId,
+    );
 
-    final outputModuleName = options.moduleNameForId(
+    final outputModuleName = WasmCompilerOptions.moduleNameForId(
       options.outputFile,
       moduleId,
     );
@@ -224,7 +227,7 @@ class CompilerPhaseInputOutputManager {
     final moduleIds = <int>{};
     for (final file in files) {
       if (file is! File) continue;
-      final moduleId = options.idForModuleName(
+      final moduleId = WasmCompilerOptions.idForModuleName(
         mainWasmFilename,
         path.basename(file.path),
       );
diff --git a/pkg/dart2wasm/lib/kernel_nodes.dart b/pkg/dart2wasm/lib/kernel_nodes.dart
index d72abd0fd9b..fc089b429ca 100644
--- a/pkg/dart2wasm/lib/kernel_nodes.dart
+++ b/pkg/dart2wasm/lib/kernel_nodes.dart
@@ -774,6 +774,12 @@ mixin KernelNodes {
     LibraryIndex.topLevel,
     'get:_loadingMap',
   );
+  late final Procedure? dartInternalModuleNamePrefixGetter = index
+      .tryGetProcedure(
+        'dart:_internal',
+        LibraryIndex.topLevel,
+        'get:_moduleNamePrefix',
+      );
   late final Procedure? dartInternalLoadingMapNamesGetter = index
       .tryGetProcedure(
         'dart:_internal',
diff --git a/pkg/dart2wasm/lib/modules.dart b/pkg/dart2wasm/lib/modules.dart
index 89d4ec0087b..cbb43298b14 100644
--- a/pkg/dart2wasm/lib/modules.dart
+++ b/pkg/dart2wasm/lib/modules.dart
@@ -37,7 +37,11 @@ class ModuleMetadataBuilder {
         : 'module$id';
     return ModuleMetadata._(
       moduleImportName,
-      options.moduleNameForId(options.outputFile, id, emitAsMain: emitAsMain),
+      WasmCompilerOptions.moduleNameForId(
+        options.outputFile,
+        id,
+        emitAsMain: emitAsMain,
+      ),
       skipEmit: skipEmit,
       isMain: id == WasmCompilerOptions.mainModuleId,
     );
diff --git a/pkg/dart2wasm/lib/translator.dart b/pkg/dart2wasm/lib/translator.dart
index 06ac6521be6..728a7470474 100644
--- a/pkg/dart2wasm/lib/translator.dart
+++ b/pkg/dart2wasm/lib/translator.dart
@@ -28,6 +28,7 @@ import 'dispatch_table.dart';
 import 'dynamic_dispatch_table.dart';
 import 'dynamic_dispatchers.dart';
 import 'functions.dart';
+import 'generate_wasm.dart';
 import 'globals.dart';
 import 'kernel_nodes.dart';
 import 'modules.dart';
@@ -645,40 +646,85 @@ class Translator with KernelNodes {
   // NOTE: We do this after code generation is complete. So the code generation
   // phase has the opportunity to generate more wasm modules and add them to the
   // loading map.
+  //
+  // Keep in sync with sdk/lib/_internal/wasm/js_common/deferred_patch.dart's
+  // `_decodeEncodedModuleIds` and `_loadLibraryViaEmbedderModuleNames`
   void _patchLoadingMapGetter(w.FunctionBuilder function) {
-    final externRef = w.RefType.extern(nullable: false);
-    final arrayExternRef = wasmArrayType(
-      externRef,
-      externRef.toString(),
-      mutable: false,
-    );
-    final arrayArrayString = wasmArrayType(
-      w.RefType(arrayExternRef, nullable: false),
-      arrayExternRef.toString(),
-      mutable: false,
+    final moduleMap = loadingMap.moduleMap;
+    final byteArrayType = wasmArrayType(w.PackedType.i8, 'WasmI8');
+    final arrayOfNullableByteArray = wasmArrayType(
+      w.RefType(byteArrayType, nullable: true),
+      'WasmArray<WasmI8>',
     );
 
-    _lazyInitializeGlobal(
-      function,
-      w.RefType(arrayArrayString, nullable: false),
-      'loadIdModuleNames',
-      (b) {
-        final moduleMap = loadingMap.moduleMap;
-        for (int i = 0; i < moduleMap.length; ++i) {
-          final moduleNames = moduleMap[i];
-          for (int k = 0; k < moduleNames.length; ++k) {
-            b.global_get(
-              getInternalizedStringGlobal(
-                function.moduleBuilder,
-                moduleNames[k].moduleName,
-              ),
-            );
-          }
-          b.array_new_fixed(arrayExternRef, moduleNames.length);
-        }
-        b.array_new_fixed(arrayArrayString, moduleMap.length);
-      },
+    // Make a global containing the load id -> module id list table.
+    final loadingMapGlobal = mainModule.globals.define(
+      w.GlobalType(w.RefType(arrayOfNullableByteArray, nullable: false)),
     );
+    loadingMapGlobal.initializer
+      ..i32_const(moduleMap.length)
+      ..array_new_default(arrayOfNullableByteArray)
+      ..end();
+
+    // Make the getter return that array.
+    _replaceBody(function)
+      ..global_get(loadingMapGlobal)
+      ..end();
+
+    // Emit code to initialize the load id -> module id list table.
+    final startFunction = mainModule.startFunction.body;
+    final encodedSegment = mainModule.dataSegments.define();
+    for (int i = 0; i < moduleMap.length; ++i) {
+      final moduleNames = moduleMap[i];
+      if (moduleNames.isEmpty) continue;
+
+      // We sort the module ids increasingly, thereby allowing us to encode them
+      // via delta to previous module id.
+      final moduleIds = <int>[];
+      for (int k = 0; k < moduleNames.length; ++k) {
+        final moduleId = WasmCompilerOptions.idFromDeferredModuleFilename(
+          moduleNames[k].moduleName,
+        );
+        moduleIds.add(moduleId);
+      }
+      moduleIds.sort();
+
+      // Make the encoded list of module ids.
+      final moduleIdsEncoded = BytesBuilder();
+      moduleIdsEncoded.writeULEB128(moduleNames.length);
+      int lastId = 0;
+      for (int i = 0; i < moduleIds.length; ++i) {
+        final moduleId = moduleIds[i];
+        final diff = moduleId - lastId;
+        moduleIdsEncoded.writeULEB128(diff);
+        lastId = moduleId;
+      }
+
+      // Append the encoded module id list to the data segment & make start
+      // function patch the runtime with the list.
+      startFunction.global_get(loadingMapGlobal);
+      startFunction.i32_const(i);
+      {
+        startFunction.i32_const(encodedSegment.length);
+        startFunction.i32_const(moduleIdsEncoded.length);
+        startFunction.array_new_data(byteArrayType, encodedSegment);
+        encodedSegment.append(moduleIdsEncoded.takeBytes());
+      }
+      startFunction.array_set(arrayOfNullableByteArray);
+    }
+
+    final mainModuleOutput = _builderToOutput[mainModule]!;
+    final prefix = WasmCompilerOptions.deferredModuleFilenamePrefix(
+      mainModuleOutput.moduleName,
+    );
+    final prefixGetter =
+        functions.getExistingFunction(
+              dartInternalModuleNamePrefixGetter!.reference,
+            )
+            as w.FunctionBuilder;
+    _replaceBody(prefixGetter)
+      ..global_get(getInternalizedStringGlobal(mainModule, prefix))
+      ..end();
   }
 
   void _patchLoadingMapNamesGetter(w.FunctionBuilder function) {
@@ -724,12 +770,7 @@ class Translator with KernelNodes {
       ..ref_null(w.HeapType.none)
       ..end();
 
-    final b = w.InstructionsBuilder(
-      f.moduleBuilder,
-      f.type.inputs,
-      f.type.outputs,
-    );
-    f.replaceBody(b);
+    final b = _replaceBody(f);
 
     final label = b.block(const [], [type]);
     b.global_get(global);
@@ -743,6 +784,16 @@ class Translator with KernelNodes {
     b.end();
   }
 
+  w.InstructionsBuilder _replaceBody(w.FunctionBuilder function) {
+    final newBody = w.InstructionsBuilder(
+      function.moduleBuilder,
+      function.type.inputs,
+      function.type.outputs,
+    );
+    function.replaceBody(newBody);
+    return newBody;
+  }
+
   void _printFunction(w.BaseFunction function, Object name) {
     if (options.printWasm) {
       print("#${function.name}: $name");
@@ -3968,3 +4019,15 @@ class SingleClosureTarget {
 
   SingleClosureTarget._(this.callTarget, this.paramInfo);
 }
+
+extension on BytesBuilder {
+  void writeULEB128(int value) {
+    assert(value >= 0);
+    do {
+      int byte = value & 0x7F;
+      value >>>= 7;
+      if (value != 0) byte |= 0x80;
+      addByte(byte);
+    } while (value != 0);
+  }
+}
diff --git a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.constraints.txt b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.constraints.txt
index 06027de75a4..db7cc27a906 100644
--- a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.constraints.txt
+++ b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.constraints.txt
@@ -55,7 +55,6 @@ Part 0
      - pkg/compiler/test/custom_split/data/fuse_with_and/lib_010_0.dart::@methods::g_010_0
      - pkg/compiler/test/custom_split/data/fuse_with_and/lib_100_0.dart::@methods::g_100_0
   Constants
-     - IntConstant(127)
      - IntConstant(20)
      - IntConstant(256)
      - IntConstant(36)
diff --git a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.default.txt b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.default.txt
index 949df457003..a9be2a91bcc 100644
--- a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.default.txt
+++ b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_and.default.txt
@@ -39,7 +39,6 @@ Part 0
      - pkg/compiler/test/custom_split/data/fuse_with_and/libImport.dart::@methods::f_111_1
      - pkg/compiler/test/custom_split/data/fuse_with_and/libImport.dart::@methods::v
   Constants
-     - IntConstant(127)
      - IntConstant(20)
      - IntConstant(256)
      - IntConstant(36)
diff --git a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.constraints.txt b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.constraints.txt
index e8a0bd51f83..454a2915094 100644
--- a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.constraints.txt
+++ b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.constraints.txt
@@ -49,7 +49,6 @@ Part 0
      - pkg/compiler/test/custom_split/data/fuse_with_or/libImport.dart::@methods::v
      - pkg/compiler/test/custom_split/data/fuse_with_or/lib_001_0.dart::@methods::g_001_0
   Constants
-     - IntConstant(127)
      - IntConstant(20)
      - IntConstant(256)
      - IntConstant(36)
diff --git a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.default.txt b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.default.txt
index 64fe2643f8c..a5aa9fec2e1 100644
--- a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.default.txt
+++ b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/fuse_with_or.default.txt
@@ -39,7 +39,6 @@ Part 0
      - pkg/compiler/test/custom_split/data/fuse_with_or/libImport.dart::@methods::f_111_1
      - pkg/compiler/test/custom_split/data/fuse_with_or/libImport.dart::@methods::v
   Constants
-     - IntConstant(127)
      - IntConstant(20)
      - IntConstant(256)
      - IntConstant(36)
diff --git a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.constraints.txt b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.constraints.txt
index d8533f0f1cd..c6a25c84ec3 100644
--- a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.constraints.txt
+++ b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.constraints.txt
@@ -41,7 +41,6 @@ Part 0
      - pkg/compiler/test/custom_split/data/just_fuse/libImport.dart::@methods::f_111_1
      - pkg/compiler/test/custom_split/data/just_fuse/libImport.dart::@methods::v
   Constants
-     - IntConstant(127)
      - IntConstant(20)
      - IntConstant(256)
      - IntConstant(36)
diff --git a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.default.txt b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.default.txt
index fa1755cd53b..99b0495ef3e 100644
--- a/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.default.txt
+++ b/pkg/dart2wasm/test/deferred_loading/partition_tests_dart2js/custom_split/just_fuse.default.txt
@@ -39,7 +39,6 @@ Part 0
      - pkg/compiler/test/custom_split/data/just_fuse/libImport.dart::@methods::f_111_1
      - pkg/compiler/test/custom_split/data/just_fuse/libImport.dart::@methods::v
   Constants
-     - IntConstant(127)
      - IntConstant(20)
      - IntConstant(256)
      - IntConstant(36)
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module1.wat b/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module1.wat
index fcb344a4470..84f5203cfbf 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module1.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module1.wat
@@ -16,7 +16,7 @@
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 17 funcref)
   (global $"\"bad\"" (ref $JSExternWrapper) <...>)
   (global $MyConstClass (ref $MyConstClass)
-    (i32.const 108)
+    (i32.const 109)
     (i32.const 0)
     (i32.const 60)
     (i32.const 0)
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module2.wat b/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module2.wat
index 7da3ac8a14b..0c371d831ba 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module2.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module2.wat
@@ -15,7 +15,7 @@
   (global $.h0-nonshared-const (import "" "h0-nonshared-const") (ref extern))
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 17 funcref)
   (global $MyConstClass (ref $MyConstClass)
-    (i32.const 108)
+    (i32.const 109)
     (i32.const 0)
     (i32.const 60)
     (i32.const 0)
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module3.wat b/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module3.wat
index 1c54c08596b..31caaef9927 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module3.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.constant.multi_module_use_module3.wat
@@ -14,7 +14,7 @@
     (field $field1 (mut i32)))))
   (global $.shared-const (import "" "shared-const") (ref extern))
   (global $MyConstClass (ref $MyConstClass)
-    (i32.const 108)
+    (i32.const 109)
     (i32.const 0)
     (i32.const 60)
     (i32.const 0)
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.constant.type_use_module1.wat b/pkg/dart2wasm/test/ir_tests/deferred.constant.type_use_module1.wat
index 87304e7697e..6f979101a1e 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.constant.type_use_module1.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.constant.type_use_module1.wat
@@ -10,7 +10,7 @@
   (global $".Foo called " (import "" "Foo called ") (ref extern))
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 4 funcref)
   (global $"\"Foo called \"" (ref $JSExternWrapper)
-    (i32.const 58)
+    (i32.const 59)
     (i32.const 0)
     (global.get $".Foo called ")
     (struct.new $JSExternWrapper))
@@ -27,7 +27,7 @@
   )
   (func $"useFooAsObject <noInline>"
     (local $var0 (ref $Foo))
-    i32.const 106
+    i32.const 107
     i32.const 0
     i64.const 0
     struct.new $Foo
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.constant_module1.wat b/pkg/dart2wasm/test/ir_tests/deferred.constant_module1.wat
index 4f931842ac4..9c2ca81fd74 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.constant_module1.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.constant_module1.wat
@@ -58,7 +58,7 @@
     (local $var1 (ref $_FunctionType))
     (local $var2 (ref $#Closure-0-1))
     (local $var3 (ref $H1))
-    i32.const 106
+    i32.const 107
     i32.const 0
     block $label0 (result (ref $#Closure-0-1))
       global.get $"InstantiationConstant(globalH1Foo<int>)"
@@ -144,7 +144,7 @@
     struct.get $H1 $fun
     local.tee $var0
     struct.get $#Closure-0-1 $context
-    i32.const 86
+    i32.const 88
     i64.const 1
     struct.new $BoxedInt
     local.get $var0
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.constant_module2.wat b/pkg/dart2wasm/test/ir_tests/deferred.constant_module2.wat
index f8fc0efc04e..e9b9009d8c9 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.constant_module2.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.constant_module2.wat
@@ -39,7 +39,7 @@
     (local $var0 (ref $_FunctionType))
     (local $var1 (ref $#Closure-0-1))
     (local $var2 (ref $H0))
-    i32.const 107
+    i32.const 108
     i32.const 0
     block $label0 (result (ref $#Closure-0-1))
       global.get $"globalH0Foo tear-off"
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.devirtualized_module1.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.devirtualized_module1.wat
index 51a13f85e41..71e479d1ff1 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.devirtualized_module1.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.devirtualized_module1.wat
@@ -11,7 +11,7 @@
   (global $1 (import "module0" "global2") (ref $BoxedInt))
   (global $2 (import "module0" "global3") (ref $BoxedInt))
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 18 funcref)
-  (table $module0.dispatch0 (import "module0" "dispatch0") 654 funcref)
+  (table $module0.dispatch0 (import "module0" "dispatch0") 657 funcref)
   (global $"\"Foo0.doitDispatch(\"" (ref $JSExternWrapper)
     (i32.const 60)
     (i32.const 0)
@@ -42,7 +42,7 @@
   (func $"foo0 <noInline>"
     call $"runtimeTrue implicit getter"
     if (result (ref $Object))
-      i32.const 108
+      i32.const 109
       i32.const 0
       struct.new $Object
     else
@@ -71,7 +71,7 @@
       global.get $1
       local.get $var0
       struct.get $Object $field0
-      i32.const 365
+      i32.const 399
       i32.add
       call_indirect $module0.dispatch0 (param (ref $Object) (ref null $#Top))
       block $label2 (result (ref $Object))
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.wat
index 49689cd4414..8a3076f7b5b 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained.wat
@@ -22,7 +22,7 @@
   (global $"\"foo0Code(\"" (ref $JSExternWrapper) <...>)
   (global $0 (ref $BoxedInt) <...>)
   (global $FooConst0 (ref $Object)
-    (i32.const 108)
+    (i32.const 109)
     (i32.const 0)
     (struct.new $Object))
   (global $fooGlobal0 (mut (ref null $#Top))
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module2.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module2.wat
index 702a07795ab..32ab0f730d0 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module2.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module2.wat
@@ -8,7 +8,7 @@
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 45 funcref)
   (global $"\"foo1Code(\"" (ref $JSExternWrapper) <...>)
   (global $FooConst1 (ref $Object)
-    (i32.const 109)
+    (i32.const 110)
     (i32.const 0)
     (struct.new $Object))
   (global $fooGlobal1 (mut (ref null $#Top))
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module3.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module3.wat
index bdc638c970d..2c8761e2395 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module3.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module3.wat
@@ -22,7 +22,7 @@
   (global $FooConst0 (import "module0" "global7") (ref $Object))
   (global $fooGlobal0 (import "module0" "global16") (ref null $#Top))
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 45 funcref)
-  (table $module0.dispatch0 (import "module0" "dispatch0") 670 funcref)
+  (table $module0.dispatch0 (import "module0" "dispatch0") 673 funcref)
   (global $"\"0\"" (ref $JSExternWrapper) <...>)
   (global $"\"1\"" (ref $JSExternWrapper) <...>)
   (global $"\"2\"" (ref $JSExternWrapper) <...>)
@@ -65,7 +65,7 @@
     (struct.new $JSExternWrapper))
   (global $"\"foo5Code(\"" (ref $JSExternWrapper) <...>)
   (global $FooConst5 (ref $Object)
-    (i32.const 113)
+    (i32.const 114)
     (i32.const 0)
     (struct.new $Object))
   (global $_InterfaceType (ref $_InterfaceType) <...>)
@@ -222,7 +222,7 @@
     call $"fooGlobal5 implicit getter"
     local.get $var2
     struct.get $Object $field0
-    i32.const 378
+    i32.const 382
     i32.add
     call_indirect $module0.dispatch0 (param (ref $Object) (ref null $#Top))
   )
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module5.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module5.wat
index 3bd1dfd66cd..5a945546f5d 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module5.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module5.wat
@@ -8,7 +8,7 @@
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 45 funcref)
   (global $"\"foo2Code(\"" (ref $JSExternWrapper) <...>)
   (global $FooConst2 (ref $Object)
-    (i32.const 110)
+    (i32.const 111)
     (i32.const 0)
     (struct.new $Object))
   (global $fooGlobal2 (mut (ref null $#Top))
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module7.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module7.wat
index 91d84286c92..1c5535f048f 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module7.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module7.wat
@@ -8,7 +8,7 @@
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 45 funcref)
   (global $"\"foo3Code(\"" (ref $JSExternWrapper) <...>)
   (global $FooConst3 (ref $Object)
-    (i32.const 111)
+    (i32.const 112)
     (i32.const 0)
     (struct.new $Object))
   (global $fooGlobal3 (mut (ref null $#Top))
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module9.wat b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module9.wat
index 52ff5f56959..661f8fb5d1c 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module9.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.fine_grained_module9.wat
@@ -8,7 +8,7 @@
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 45 funcref)
   (global $"\"foo4Code(\"" (ref $JSExternWrapper) <...>)
   (global $FooConst4 (ref $Object)
-    (i32.const 112)
+    (i32.const 113)
     (i32.const 0)
     (struct.new $Object))
   (global $fooGlobal4 (mut (ref null $#Top))
diff --git a/pkg/dart2wasm/test/ir_tests/deferred.init_at_startup.wat b/pkg/dart2wasm/test/ir_tests/deferred.init_at_startup.wat
index 87dcbc86c7d..29b2ce9b1fa 100644
--- a/pkg/dart2wasm/test/ir_tests/deferred.init_at_startup.wat
+++ b/pkg/dart2wasm/test/ir_tests/deferred.init_at_startup.wat
@@ -3,6 +3,8 @@
   (type $ArgumentError <...>)
   (type $Array<Object?> <...>)
   (type $Array<String> <...>)
+  (type $Array<WasmArray<WasmI8>?> <...>)
+  (type $Array<WasmI8> <...>)
   (type $Array<int> <...>)
   (type $JSExternWrapper <...>)
   (type $Object <...>)
@@ -16,6 +18,7 @@
   (global $BoxedDouble._cacheKeys (mut (ref $Array<int>)) <...>)
   (global $BoxedDouble._cacheValues (mut (ref $Array<String>)) <...>)
   (global $_deletedDataMarker (mut (ref $#Top)) <...>)
+  (global $global0 (ref $Array<WasmArray<WasmI8>?>) <...>)
   (elem $cross-module-funcs-0
     (set 3 (ref.func $"wasm:js-string.length (import)"))
     (set 4 (ref.func $JSStringImpl._interpolate))
@@ -49,6 +52,12 @@
     i32.const 0
     struct.new $Object
     global.set $_deletedDataMarker
+    global.get $global0
+    i32.const 0
+    i32.const 0
+    i32.const 2
+    array.new_data $Array<WasmI8>$data0
+    array.set $Array<WasmArray<WasmI8>?>
   )
   (func $ArgumentError (param $var0 (ref null $#Top)) (param $var1 (ref null $JSExternWrapper)) (result (ref $ArgumentError)) <...>)
   (func $IntegerDivisionByZeroException (result (ref $Object)) <...>)
@@ -58,4 +67,5 @@
   (func $JSStringImpl.fromRefUnchecked (param $var0 externref) (result (ref $JSExternWrapper)) <...>)
   (func $JSStringImpl.substring (param $var0 (ref $JSExternWrapper)) (param $var1 i64) (param $var2 i64) (result (ref $JSExternWrapper)) <...>)
   (func $_jsBigIntToString (param $var0 i64) (param $var1 i64) (result (ref $JSExternWrapper)) <...>)
+  (data $data0 <... 2 bytes ...>)
 )
\ No newline at end of file
diff --git a/pkg/dart2wasm/test/ir_tests/dispatch_table_reuse_module1.wat b/pkg/dart2wasm/test/ir_tests/dispatch_table_reuse_module1.wat
index bfa645d89b8..aee296059d5 100644
--- a/pkg/dart2wasm/test/ir_tests/dispatch_table_reuse_module1.wat
+++ b/pkg/dart2wasm/test/ir_tests/dispatch_table_reuse_module1.wat
@@ -7,7 +7,7 @@
   (type $WasmListBase <...>)
   (type $_Type <...>)
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 12 funcref)
-  (table $module0.dispatch0 (import "module0" "dispatch0") 670 funcref)
+  (table $module0.dispatch0 (import "module0" "dispatch0") 673 funcref)
   (elem $module0.cross-module-funcs-0
     (set 0 (ref.func $"runTest <noInline>")))
   (func $"runTest <noInline>"
@@ -83,19 +83,19 @@
         ref.cast $Object
         local.tee $var2
         struct.get $Object $field0
-        i32.const 109
+        i32.const 110
         i32.eq
         if
           local.get $var2
           local.get $var5
-          i32.const 487
+          i32.const 492
           call_indirect $module0.dispatch0 (param (ref $Object) i64)
         else
           local.get $var2
           local.get $var5
           local.get $var2
           struct.get $Object $field0
-          i32.const 378
+          i32.const 382
           i32.add
           call_indirect $module0.dispatch0 (param (ref $Object) i64)
         end
diff --git a/pkg/dart2wasm/test/ir_tests/import_name_module1.wat b/pkg/dart2wasm/test/ir_tests/import_name_module1.wat
index 051bb9de685..a2c22eb15f0 100644
--- a/pkg/dart2wasm/test/ir_tests/import_name_module1.wat
+++ b/pkg/dart2wasm/test/ir_tests/import_name_module1.wat
@@ -11,7 +11,7 @@
   (global $".hello world" (import "" "hello world") (ref extern))
   (table $module0.cross-module-funcs-0 (import "module0" "cross-module-funcs-0") 2 funcref)
   (global $"\"hello world\"" (ref $JSExternWrapper)
-    (i32.const 57)
+    (i32.const 59)
     (i32.const 0)
     (global.get $".hello world")
     (struct.new $JSExternWrapper))
diff --git a/sdk/lib/_internal/wasm/js_common/deferred_patch.dart b/sdk/lib/_internal/wasm/js_common/deferred_patch.dart
index 78e5b72d97f..a0041efcc28 100644
--- a/sdk/lib/_internal/wasm/js_common/deferred_patch.dart
+++ b/sdk/lib/_internal/wasm/js_common/deferred_patch.dart
@@ -22,11 +22,19 @@ final Map<int, Future<void>> _loading = {};
 final Set<int> _loaded = {};
 
 /// Only used when loading modules directly, will get populated by the compiler.
-external ImmutableWasmArray<ImmutableWasmArray<WasmExternRef>> get _loadingMap;
+///
+/// Maps a loading id (aka deferred prefix) to the set of module ids that have
+/// to be loaded.
+external WasmArray<WasmArray<WasmI8>?> get _loadingMap;
 
 /// Maps load id to (import uri, import prefix).
 external ImmutableWasmArray<WasmExternRef> get _loadingMapNames;
 
+/// The prefix of all module names.
+///
+/// For `test_module<id>.wasm` it will be `test_module`.
+external WasmExternRef get _moduleNamePrefix;
+
 @pragma("wasm:import", "moduleLoadingHelper.loadDeferredModules")
 external WasmExternRef _loadDeferredModules(WasmExternRef moduleNames);
 
@@ -94,8 +102,10 @@ Future<void> loadLibraryFromLoadId(int loadId) {
           'Error loading load ID: ${_loadIdInJson(loadId)}\n$e',
         );
       }
-      return 'Error loading ${_prefixName(loadId)} of library '
-          '${_importUri(loadId)}\n$e';
+      throw DeferredLoadException(
+        'Error loading ${_prefixName(loadId)} of library '
+        '${_importUri(loadId)}\n$e',
+      );
     },
   );
 }
@@ -108,18 +118,47 @@ Future<void> _loadLibraryViaEmbedderLoadId(int loadId) {
 
 Future<void> _loadLibraryViaEmbedderModuleNames(int loadId) {
   assert(loadId < _loadingMap.length);
-
-  final ImmutableWasmArray<WasmExternRef> moduleNames = _loadingMap[loadId];
-  if (moduleNames.length == 0) {
+  final WasmArray<WasmI8>? encodedModuleIds = _loadingMap[loadId];
+  if (encodedModuleIds == null) {
     // No modules to load.
     return Future.value();
   }
-  final moduleNamesAsList = <JSString>[];
-  for (int i = 0; i < moduleNames.length; ++i) {
-    moduleNamesAsList.add(JSValue(moduleNames[i]) as JSString);
-  }
+  final moduleNamesAsList = _decodeEncodedModuleIds('test', encodedModuleIds);
+
   final promise =
       (_loadDeferredModules(moduleNamesAsList.toJS.toExternRef!).toJS
           as JSPromise);
   return promise.toDart;
 }
+
+/// Keep in sync with pkg/dart2wasm/lib/translator.dart:Translator._patchLoadingMapGetter`
+List<JSString> _decodeEncodedModuleIds(
+  String prefix,
+  WasmArray<WasmI8> encoded,
+) {
+  int offset = 0;
+
+  int nextULEB128() {
+    int result = 0;
+    int shift = 0;
+    while (true) {
+      final byte = encoded.readUnsigned(offset++);
+      result |= (byte & 0x7F) << shift;
+      shift += 7;
+      if ((byte & 0x80) == 0) break;
+    }
+    return result;
+  }
+
+  final length = nextULEB128();
+  final moduleIds = <JSString>[];
+  int previousModuleId = 0;
+  final prefix = JSStringImpl.fromRefUnchecked(_moduleNamePrefix);
+  for (int i = 0; i < length; ++i) {
+    int diff = nextULEB128();
+    final moduleId = previousModuleId + diff;
+    moduleIds.add('$prefix${moduleId.toString()}.wasm'.toJS);
+    previousModuleId = moduleId;
+  }
+  return moduleIds;
+}