diff --git a/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_strong_script.dart b/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_strong_script.dart
new file mode 100644
index 00000000000..08214612fdd
--- /dev/null
+++ b/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_strong_script.dart
@@ -0,0 +1,29 @@
+// Copyright (c) 2020, 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 script for type_casts_with_null_safety_autodetection_test.dart which
+// is supposed to run in strong mode because it is opted-in.
+
+import 'package:expect/expect.dart';
+
+dynamic nullObj;
+
+@pragma('vm:never-inline')
+typeCast<T>(x) => x as T;
+
+doTests() {
+  typeCast<dynamic>(nullObj);
+  typeCast<void>(nullObj);
+  Expect.throwsTypeError(() => typeCast<Object>(nullObj));
+  Expect.throwsTypeError(() => typeCast<int>(nullObj));
+  typeCast<List<int>>(<int>[]);
+  Expect.throwsTypeError(() => typeCast<List<int>>(<Null>[]));
+}
+
+main() {
+  for (int i = 0; i < 20; ++i) {
+    doTests();
+  }
+  print('OK(strong)');
+}
diff --git a/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_test.dart b/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_test.dart
new file mode 100644
index 00000000000..701f409ef12
--- /dev/null
+++ b/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_test.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2020, 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.
+
+// OtherResources=type_casts_with_null_safety_autodetection_strong_script.dart
+// OtherResources=type_casts_with_null_safety_autodetection_weak_script.dart
+
+// This test verifies that casts with type testing stubs work as expected
+// if null safety mode (weak/strong) is auto-detected.
+
+import 'dart:io' show File, Platform;
+
+import 'package:path/path.dart' as path;
+import 'snapshot_test_helper.dart';
+
+runTest(String script, String output, String temp) async {
+  // Need to copy test scripts out of Dart SDK to avoid hardcoded
+  // opted-in/opted-out status for Dart SDK tests.
+  final scriptInTemp = path.join(temp, script);
+  File.fromUri(Platform.script.resolve(script)).copySync(scriptInTemp);
+
+  // Do not add Platform.executableArguments into arguments to avoid passing
+  // --null-safety / --no-null-safety arguments.
+  final result = await runBinary("RUN $script", Platform.executable, [
+    '--enable-experiment=non-nullable',
+    '--deterministic',
+    '--optimization-counter-threshold=10',
+    '--packages=${Platform.packageConfig}',
+    scriptInTemp,
+  ]);
+  expectOutput(output, result);
+}
+
+main() async {
+  await withTempDir((String temp) async {
+    await runTest(
+        'type_casts_with_null_safety_autodetection_strong_script.dart',
+        'OK(strong)',
+        temp);
+    await runTest('type_casts_with_null_safety_autodetection_weak_script.dart',
+        'OK(weak)', temp);
+  });
+}
diff --git a/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_weak_script.dart b/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_weak_script.dart
new file mode 100644
index 00000000000..a12eacd91ad
--- /dev/null
+++ b/runtime/tests/vm/dart/type_casts_with_null_safety_autodetection_weak_script.dart
@@ -0,0 +1,31 @@
+// Copyright (c) 2020, 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 script for type_casts_with_null_safety_autodetection_test.dart which
+// is supposed to run in weak mode because it is opted-out.
+
+// @dart=2.6
+
+import 'package:expect/expect.dart';
+
+dynamic nullObj;
+
+@pragma('vm:never-inline')
+typeCast<T>(x) => x as T;
+
+void doTests() {
+  typeCast<dynamic>(nullObj);
+  typeCast<void>(nullObj);
+  typeCast<Object>(nullObj);
+  typeCast<int>(nullObj);
+  typeCast<List<int>>(<int>[]);
+  typeCast<List<int>>(<Null>[]);
+}
+
+main() {
+  for (int i = 0; i < 20; ++i) {
+    doTests();
+  }
+  print('OK(weak)');
+}
diff --git a/runtime/tests/vm/vm.status b/runtime/tests/vm/vm.status
index c8912f5999e..72ce9c8371b 100644
--- a/runtime/tests/vm/vm.status
+++ b/runtime/tests/vm/vm.status
@@ -248,6 +248,7 @@ dart/minimal_kernel_bytecode_test: SkipByDesign # Test needs to run from source
 dart/minimal_kernel_test: SkipByDesign # Test needs to run from source
 dart/null_safety_autodetection_in_kernel_compiler_test: SkipByDesign # Test needs to run from source
 dart/snapshot_depfile_test: SkipByDesign # Test needs to run from source
+dart/type_casts_with_null_safety_autodetection_test: SkipByDesign # Test needs to run from source
 dart_2/appjit*: SkipByDesign # Test needs to run from source
 dart_2/bytecode_and_ast_mix_test: SkipByDesign # Test needs to run from source
 dart_2/kernel_determinism_test: SkipByDesign # Test needs to run from source
diff --git a/runtime/vm/dart_entry.cc b/runtime/vm/dart_entry.cc
index 6c306ac5af9..8a1350e6490 100644
--- a/runtime/vm/dart_entry.cc
+++ b/runtime/vm/dart_entry.cc
@@ -188,6 +188,7 @@ ObjectPtr DartEntry::InvokeCode(const Code& code,
                                 Thread* thread) {
   ASSERT(!code.IsNull());
   ASSERT(thread->no_callback_scope_depth() == 0);
+  ASSERT(!Isolate::Current()->null_safety_not_set());
 
   invokestub entrypoint =
       reinterpret_cast<invokestub>(StubCode::InvokeDartCode().EntryPoint());