diff --git a/pkg/dart2wasm/lib/class_info.dart b/pkg/dart2wasm/lib/class_info.dart
index f39e8709f7f..f99a6faced0 100644
--- a/pkg/dart2wasm/lib/class_info.dart
+++ b/pkg/dart2wasm/lib/class_info.dart
@@ -118,6 +118,9 @@ class ClassInfo {
   /// follow the Dart class hierarchy.
   final ClassInfo? superInfo;
 
+  /// The class that this class masquerades as via `runtimeType`, if any.
+  ClassInfo? masquerade = null;
+
   /// For every type parameter which is directly mapped to a type parameter in
   /// the superclass, this contains the corresponding superclass type
   /// parameter. These will reuse the corresponding type parameter field of
@@ -186,6 +189,36 @@ class ClassInfoCollector {
   /// shape class with that many fields.
   final Map<int, w.StructType> _recordStructs = {};
 
+  /// Masquerades for implementation classes. For each entry of the map, all
+  /// subtypes of the key masquerade as the value.
+  late final Map<Class, Class> _masquerades = {
+    translator.coreTypes.boolClass: translator.coreTypes.boolClass,
+    translator.coreTypes.intClass: translator.coreTypes.intClass,
+    translator.coreTypes.doubleClass: translator.coreTypes.doubleClass,
+    translator.coreTypes.stringClass: translator.coreTypes.stringClass,
+    translator.index.getClass("dart:core", "_Type"):
+        translator.coreTypes.typeClass,
+    translator.index.getClass("dart:core", "_ListBase"):
+        translator.coreTypes.listClass,
+    for (Class cls in const <String>[
+      "Int8List",
+      "Uint8List",
+      "Uint8ClampedList",
+      "Int16List",
+      "Uint16List",
+      "Int32List",
+      "Uint32List",
+      "Int64List",
+      "Uint64List",
+      "Float32List",
+      "Float64List",
+      "Int32x4List",
+      "Float32x4List",
+      "Float64x2List",
+    ].map((name) => translator.index.getClass("dart:typed_data", name)))
+      cls: cls
+  };
+
   /// Wasm field type for fields with type [_Type]. Fields of this type are
   /// added to classes for type parameters.
   ///
@@ -292,6 +325,26 @@ class ClassInfoCollector {
     translator.classes.add(info);
     translator.classInfo[cls] = info;
     translator.classForHeapType.putIfAbsent(info.struct, () => info!);
+
+    ClassInfo? computeMasquerade() {
+      if (info!.superInfo?.masquerade != null) {
+        return info.superInfo!.masquerade;
+      }
+      for (Supertype implemented in cls.implementedTypes) {
+        ClassInfo? implementedMasquerade =
+            translator.classInfo[implemented.classNode]!.masquerade;
+        if (implementedMasquerade != null) {
+          return implementedMasquerade;
+        }
+      }
+      Class? selfMasquerade = _masquerades[cls];
+      if (selfMasquerade != null) {
+        return translator.classInfo[selfMasquerade]!;
+      }
+      return null;
+    }
+
+    info.masquerade = computeMasquerade();
   }
 
   void _initializeRecordClass(Class cls) {
@@ -399,6 +452,11 @@ class ClassInfoCollector {
     // parameters.
     _initialize(translator.typeClass);
 
+    // Initialize masquerade classes to make sure they have low class IDs.
+    for (Class cls in _masquerades.values) {
+      _initialize(cls);
+    }
+
     // Initialize the record base class if we have record classes.
     if (translator.recordClasses.isNotEmpty) {
       _initialize(translator.coreTypes.recordClass);
diff --git a/pkg/dart2wasm/lib/code_generator.dart b/pkg/dart2wasm/lib/code_generator.dart
index 29afd8cc029..7449dfb0fb9 100644
--- a/pkg/dart2wasm/lib/code_generator.dart
+++ b/pkg/dart2wasm/lib/code_generator.dart
@@ -2156,7 +2156,6 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
           b.i64_const(2011);
           break;
         case "runtimeType":
-        case "_runtimeType":
           wrap(ConstantExpression(TypeLiteralConstant(NullType())), resultType);
           break;
         default:
diff --git a/pkg/dart2wasm/lib/intrinsics.dart b/pkg/dart2wasm/lib/intrinsics.dart
index 929bab8ef85..044d29cb2de 100644
--- a/pkg/dart2wasm/lib/intrinsics.dart
+++ b/pkg/dart2wasm/lib/intrinsics.dart
@@ -694,25 +694,6 @@ class Intrinsifier {
           return translator.types.makeTypeRulesSubstitutions(b);
         case "_getTypeNames":
           return translator.types.makeTypeNames(b);
-        case "_getFunctionTypeRuntimeType":
-          Expression object = node.arguments.positional[0];
-          w.StructType closureBase =
-              translator.closureLayouter.closureBaseStruct;
-          codeGen.wrap(object, w.RefType.def(closureBase, nullable: false));
-          b.struct_get(closureBase, FieldIndex.closureRuntimeType);
-          return translator.types.typeClassInfo.nonNullableType;
-        case "_getInterfaceTypeRuntimeType":
-          Expression object = node.arguments.positional[0];
-          Expression typeArguments = node.arguments.positional[1];
-          ClassInfo info = translator.classInfo[translator.interfaceTypeClass]!;
-          b.i32_const(info.classId);
-          b.i32_const(initialIdentityHash);
-          // Runtime types are never nullable.
-          b.i32_const(0);
-          getID(object);
-          codeGen.wrap(typeArguments, translator.types.typeListExpectedType);
-          b.struct_new(info.struct);
-          return info.nonNullableType;
       }
     }
 
@@ -1148,16 +1129,89 @@ class Intrinsifier {
     // Object.runtimeType
     if (member.enclosingClass == translator.coreTypes.objectClass &&
         name == "runtimeType") {
-      // Simple redirect to `_runtimeType`. This is done to keep
-      // `Object.runtimeType` external, which seems to be necessary for the TFA.
-      // If we don't do this, then the TFA assumes things like
-      // `null.runtimeType` are impossible and inserts a throw.
+      // Simple redirect to `_getMasqueradedRuntimeType`. This is done to keep
+      // `Object.runtimeType` external. If `Object.runtimeType` is implemented
+      // in Dart, the TFA will conclude that `null.runtimeType` never returns,
+      // since it dispatches to `Object.runtimeType`, which uses the receiver
+      // as non-nullable.
       w.Local receiver = paramLocals[0];
       b.local_get(receiver);
-      codeGen.call(translator.objectRuntimeType.reference);
+      codeGen.call(translator.getMasqueradedRuntimeType.reference);
       return true;
     }
 
+    // _getActualRuntimeType and _getMasqueradedRuntimeType
+    if (member.enclosingLibrary == translator.coreTypes.coreLibrary &&
+        (name == "_getActualRuntimeType" ||
+            name == "_getMasqueradedRuntimeType")) {
+      final bool masqueraded = name == "_getMasqueradedRuntimeType";
+
+      final w.Local object = paramLocals[0];
+      final w.Local classId = function.addLocal(w.NumType.i32);
+      final w.Local resultClassId = function.addLocal(w.NumType.i32);
+
+      w.Label interfaceType = b.block();
+      w.Label notMasqueraded = b.block();
+      w.Label recordType = b.block();
+      w.Label functionType = b.block();
+      w.Label abstractClass = b.block();
+
+      // Look up the type category by class ID and switch on it.
+      b.global_get(translator.types.typeCategoryTable);
+      b.local_get(object);
+      b.struct_get(translator.topInfo.struct, FieldIndex.classId);
+      b.local_tee(classId);
+      b.array_get_u((translator.types.typeCategoryTable.type.type as w.RefType)
+          .heapType as w.ArrayType);
+      b.local_tee(resultClassId);
+      b.br_table([
+        abstractClass,
+        functionType,
+        recordType,
+        if (masqueraded) notMasqueraded
+      ], masqueraded ? interfaceType : notMasqueraded);
+
+      b.end(); // abstractClass
+      // We should never see class IDs for abstract types.
+      b.unreachable();
+
+      b.end(); // functionType
+      w.StructType closureBase = translator.closureLayouter.closureBaseStruct;
+      b.local_get(object);
+      b.ref_cast(w.RefType.def(closureBase, nullable: false));
+      b.struct_get(closureBase, FieldIndex.closureRuntimeType);
+      b.return_();
+
+      b.end(); // recordType
+      b.local_get(object);
+      translator.convertType(
+          function,
+          object.type,
+          translator.classInfo[translator.coreTypes.recordClass]!.repr
+              .nonNullableType);
+      codeGen.call(translator.recordGetRecordRuntimeType.reference);
+      b.return_();
+
+      b.end(); // notMasqueraded
+      b.local_get(classId);
+      b.local_set(resultClassId);
+
+      b.end(); // interfaceType
+      ClassInfo info = translator.classInfo[translator.interfaceTypeClass]!;
+      b.i32_const(info.classId);
+      b.i32_const(initialIdentityHash);
+      // Runtime types are never nullable.
+      b.i32_const(0);
+      // Set class ID of interface type.
+      b.local_get(resultClassId);
+      b.i64_extend_i32_u();
+      // Call _typeArguments to get the list of type arguments.
+      b.local_get(object);
+      codeGen.call(translator.objectGetTypeArguments.reference);
+      b.struct_new(info.struct);
+      b.return_();
+    }
+
     // identical
     if (member == translator.coreTypes.identicalProcedure) {
       w.Local first = paramLocals[0];
diff --git a/pkg/dart2wasm/lib/kernel_nodes.dart b/pkg/dart2wasm/lib/kernel_nodes.dart
index 59caf8e8b0e..dfa1484c35a 100644
--- a/pkg/dart2wasm/lib/kernel_nodes.dart
+++ b/pkg/dart2wasm/lib/kernel_nodes.dart
@@ -162,12 +162,14 @@ mixin KernelNodes {
   // dart:core various procedures
   late final Procedure objectNoSuchMethod =
       index.getProcedure("dart:core", "Object", "noSuchMethod");
-  late final Procedure objectRuntimeType =
-      index.getProcedure("dart:core", "Object", "get:_runtimeType");
+  late final Procedure objectGetTypeArguments =
+      index.getProcedure("dart:core", "Object", "_getTypeArguments");
   late final Procedure nullToString =
       index.getProcedure("dart:core", "Object", "_nullToString");
   late final Procedure nullNoSuchMethod =
       index.getProcedure("dart:core", "Object", "_nullNoSuchMethod");
+  late final Procedure recordGetRecordRuntimeType =
+      index.getProcedure("dart:core", "Record", "_getRecordRuntimeType");
   late final Procedure stringEquals =
       index.getProcedure("dart:core", "_StringBase", "==");
   late final Procedure stringInterpolate =
@@ -212,6 +214,10 @@ mixin KernelNodes {
       index.getProcedure("dart:core", "Error", "_throw");
 
   // dart:core type procedures
+  late final Procedure getActualRuntimeType =
+      index.getTopLevelProcedure("dart:core", "_getActualRuntimeType");
+  late final Procedure getMasqueradedRuntimeType =
+      index.getTopLevelProcedure("dart:core", "_getMasqueradedRuntimeType");
   late final Procedure isSubtype =
       index.getTopLevelProcedure("dart:core", "_isSubtype");
   late final Procedure isTypeSubtype =
diff --git a/pkg/dart2wasm/lib/record_class_generator.dart b/pkg/dart2wasm/lib/record_class_generator.dart
index 0d7ecbb06b1..6749c492741 100644
--- a/pkg/dart2wasm/lib/record_class_generator.dart
+++ b/pkg/dart2wasm/lib/record_class_generator.dart
@@ -30,14 +30,14 @@ import 'package:dart2wasm/records.dart';
 ///   Record_2_a(this.$1, this.$2, this.a);
 ///
 ///   @pragma('wasm:entry-point')
-///   _Type get _runtimeType =>
-///     // Uses of `runtimeType` below will be fixed with #51134.
+///   _Type get _recordRuntimeType =>
 ///     _RecordType(
 ///       const ["a"],
-///       [$1.runtimeType, $2.runtimeType, a.runtimeType]);
-///
-///   @pragma('wasm:entry-point')
-///   Type get runtimeType => _runtimeType;
+///       [
+///         _getMasqueradedRuntimeTypeNullable($1),
+///         _getMasqueradedRuntimeTypeNullable($2),
+///         _getMasqueradedRuntimeTypeNullable(a)
+///       ]);
 ///
 ///   @pragma('wasm:entry-point')
 ///   String toString() =>
@@ -73,9 +73,6 @@ class _RecordClassGenerator {
   late final Class recordRuntimeTypeClass =
       coreTypes.index.getClass('dart:core', '_RecordType');
 
-  late final Class internalRuntimeTypeClass =
-      coreTypes.index.getClass('dart:core', '_Type');
-
   late final Constructor recordRuntimeTypeConstructor =
       recordRuntimeTypeClass.constructors.single;
 
@@ -85,9 +82,6 @@ class _RecordClassGenerator {
   late final Procedure objectHashAllProcedure =
       coreTypes.index.getProcedure('dart:core', 'Object', 'hashAll');
 
-  late final Procedure objectRuntimeTypeProcedure =
-      coreTypes.index.getProcedure('dart:core', 'Object', 'get:runtimeType');
-
   late final Procedure objectToStringProcedure =
       coreTypes.index.getProcedure('dart:core', 'Object', 'toString');
 
@@ -96,10 +90,11 @@ class _RecordClassGenerator {
   late final Procedure stringPlusProcedure =
       coreTypes.index.getProcedure('dart:core', 'String', '+');
 
-  DartType get nullableObjectType => coreTypes.objectNullableRawType;
+  late final Procedure getMasqueradedRuntimeTypeNullableProcedure = coreTypes
+      .index
+      .getTopLevelProcedure('dart:core', '_getMasqueradedRuntimeTypeNullable');
 
-  DartType get internalRuntimeTypeType =>
-      InterfaceType(internalRuntimeTypeClass, Nullability.nonNullable);
+  DartType get nullableObjectType => coreTypes.objectNullableRawType;
 
   DartType get nonNullableStringType => coreTypes.stringNonNullableRawType;
 
@@ -150,13 +145,7 @@ class _RecordClassGenerator {
     ));
     library.addClass(cls);
     cls.addProcedure(_generateEquals(shape, fields, cls));
-    final internalRuntimeType = _generateInternalRuntimeType(shape, fields);
-    // With `_runtimeType` we also need to override `runtimeType`, as
-    // `Object.runtimeType` is implemented as a direct call to
-    // `Object._runtimeType` instead of a virtual call.
-    final runtimeType = _generateRuntimeType(internalRuntimeType);
-    cls.addProcedure(internalRuntimeType);
-    cls.addProcedure(runtimeType);
+    cls.addProcedure(_generateRecordRuntimeType(shape, fields));
     return cls;
   }
 
@@ -352,8 +341,7 @@ class _RecordClassGenerator {
   }
 
   /// Generate `_Type get _runtimeType` member.
-  Procedure _generateInternalRuntimeType(
-      RecordShape shape, List<Field> fields) {
+  Procedure _generateRecordRuntimeType(RecordShape shape, List<Field> fields) {
     final List<Statement> statements = [];
 
     // const ["name1", "name2", ...]
@@ -361,16 +349,12 @@ class _RecordClassGenerator {
         nonNullableStringType,
         shape.names.map((name) => StringConstant(name)).toList()));
 
-    // Generate `this.field.runtimeType` for a given field.
-    // TODO(51134): We shouldn't use user-provided runtimeType below.
-    Expression fieldRuntimeTypeExpr(Field field) => InstanceGet(
-          InstanceAccessKind.Object,
+    Expression fieldRuntimeTypeExpr(Field field) => StaticInvocation(
+        getMasqueradedRuntimeTypeNullableProcedure,
+        Arguments([
           InstanceGet(InstanceAccessKind.Instance, ThisExpression(), field.name,
-              interfaceTarget: field, resultType: nullableObjectType),
-          objectRuntimeTypeProcedure.name,
-          interfaceTarget: objectRuntimeTypeProcedure,
-          resultType: runtimeTypeType,
-        );
+              interfaceTarget: field, resultType: nullableObjectType)
+        ]));
 
     // [this.$1.runtimeType, this.x.runtimeType, ...]
     final fieldTypesList = ListLiteral(
@@ -394,26 +378,7 @@ class _RecordClassGenerator {
     );
 
     return _addWasmEntryPointPragma(Procedure(
-      Name('_runtimeType', library),
-      ProcedureKind.Getter,
-      function,
-      fileUri: library.fileUri,
-    ));
-  }
-
-  /// Generate `Type get runtimeType member = _runtimeType;`.
-  Procedure _generateRuntimeType(Procedure internalRuntimeType) {
-    final FunctionNode function = FunctionNode(
-      ReturnStatement(InstanceGet(InstanceAccessKind.Instance, ThisExpression(),
-          internalRuntimeType.name,
-          interfaceTarget: internalRuntimeType,
-          resultType: internalRuntimeTypeType)),
-      positionalParameters: [],
-      returnType: runtimeTypeType,
-    );
-
-    return _addWasmEntryPointPragma(Procedure(
-      Name('runtimeType', library),
+      Name('_recordRuntimeType', library),
       ProcedureKind.Getter,
       function,
       fileUri: library.fileUri,
diff --git a/pkg/dart2wasm/lib/translator.dart b/pkg/dart2wasm/lib/translator.dart
index a7423de7ba4..f6adff1c11b 100644
--- a/pkg/dart2wasm/lib/translator.dart
+++ b/pkg/dart2wasm/lib/translator.dart
@@ -571,9 +571,12 @@ class Translator with KernelNodes {
         translateStorageType(type), type.toText(defaultAstTextStrategy));
   }
 
-  w.ArrayType wasmArrayType(w.StorageType type, String name) {
-    return arrayTypeCache.putIfAbsent(type,
-        () => m.addArrayType("Array<$name>", elementType: w.FieldType(type)));
+  w.ArrayType wasmArrayType(w.StorageType type, String name,
+      {bool mutable = true}) {
+    return arrayTypeCache.putIfAbsent(
+        type,
+        () => m.addArrayType("Array<$name>",
+            elementType: w.FieldType(type, mutable: mutable)));
   }
 
   /// Translate a Dart type as it should appear on parameters and returns of
diff --git a/pkg/dart2wasm/lib/types.dart b/pkg/dart2wasm/lib/types.dart
index 3d49413badc..a4402547365 100644
--- a/pkg/dart2wasm/lib/types.dart
+++ b/pkg/dart2wasm/lib/types.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:math' show max;
+import 'dart:typed_data' show Uint8List;
 
 import 'package:dart2wasm/class_info.dart';
 import 'package:dart2wasm/code_generator.dart';
@@ -13,6 +14,17 @@ import 'package:kernel/core_types.dart';
 
 import 'package:wasm_builder/wasm_builder.dart' as w;
 
+/// Values for the type category table. Entries for masqueraded classes contain
+/// the class ID of the masquerade.
+class TypeCategory {
+  static const abstractClass = 0;
+  static const function = 1;
+  static const record = 2;
+  static const notMasqueraded = 3;
+  static const minMasqueradeClassId = 4;
+  static const maxMasqueradeClassId = 63; // Leaves 2 unused bits for future use
+}
+
 class InterfaceTypeEnvironment {
   final Map<TypeParameter, int> _typeOffsets = {};
 
@@ -87,6 +99,9 @@ class Types {
   /// parameter index range of their corresponding function type.
   Map<TypeParameter, int> functionTypeParameterIndex = Map.identity();
 
+  /// An `i8` array of type category values, indexed by class ID.
+  late final w.Global typeCategoryTable = _buildTypeCategoryTable();
+
   Types(this.translator);
 
   w.ValueType classAndFieldToType(Class cls, int fieldIndex) =>
@@ -256,6 +271,53 @@ class Types {
     return expectedType;
   }
 
+  /// Build a global array of byte values used to categorize runtime types.
+  w.Global _buildTypeCategoryTable() {
+    Set<Class> recordClasses = Set.from(translator.recordClasses.values);
+    Uint8List table = Uint8List(translator.classes.length);
+    for (int i = 0; i < translator.classes.length; i++) {
+      ClassInfo info = translator.classes[i];
+      ClassInfo? masquerade = info.masquerade;
+      Class? cls = info.cls;
+      int category;
+      if (cls == null || cls.isAbstract) {
+        category = TypeCategory.abstractClass;
+      } else if (cls == translator.closureClass) {
+        category = TypeCategory.function;
+      } else if (recordClasses.contains(cls)) {
+        category = TypeCategory.record;
+      } else if (masquerade == null || masquerade.classId == i) {
+        category = TypeCategory.notMasqueraded;
+      } else {
+        // Masqueraded class
+        assert(cls.enclosingLibrary.importUri.scheme == "dart");
+        assert(cls.name.startsWith('_'));
+        assert(masquerade.classId >= TypeCategory.minMasqueradeClassId);
+        assert(masquerade.classId <= TypeCategory.maxMasqueradeClassId);
+        category = masquerade.classId;
+      }
+      table[i] = category;
+    }
+
+    w.DataSegment segment = translator.m.addDataSegment(table);
+    w.ArrayType arrayType =
+        translator.wasmArrayType(w.PackedType.i8, "const i8", mutable: false);
+    w.DefinedGlobal global = translator.m
+        .addGlobal(w.GlobalType(w.RefType.def(arrayType, nullable: false)));
+    // Initialize the global to a dummy array, since `array.new_data` is not
+    // a constant instruction and thus can't be used in the initializer.
+    global.initializer.array_new_fixed(arrayType, 0);
+    global.initializer.end();
+    // Create the actual table in the init function.
+    w.Instructions b = translator.initFunction.body;
+    b.i32_const(0);
+    b.i32_const(table.length);
+    b.array_new_data(arrayType, segment);
+    b.global_set(global);
+
+    return global;
+  }
+
   bool isFunctionTypeParameter(TypeParameterType type) =>
       type.parameter.parent == null;
 
diff --git a/sdk/lib/_internal/wasm/lib/bool.dart b/sdk/lib/_internal/wasm/lib/bool.dart
index aa2c78bd3e3..1c32642969f 100644
--- a/sdk/lib/_internal/wasm/lib/bool.dart
+++ b/sdk/lib/_internal/wasm/lib/bool.dart
@@ -4,18 +4,6 @@
 
 part of "core_patch.dart";
 
-@patch
-class bool {
-  // Note: this needs to be in `bool`, cannot be overridden in `_BoxedBool`. I
-  // suspect the problem is there's an assumption in the front-end that `bool`
-  // has one implementation class (unlike `double`, `int`, `String`) which is
-  // the `bool` class itself. So when `runtimeType` is not overridden in
-  // `bool`, in code like `x.runtimeType` where `x` is `bool`, direct call
-  // metadata says that the member is `Object.runtimeType`.
-  @override
-  Type get runtimeType => bool;
-}
-
 @pragma("wasm:entry-point")
 final class _BoxedBool extends bool {
   // A boxed bool contains an unboxed bool.
diff --git a/sdk/lib/_internal/wasm/lib/double.dart b/sdk/lib/_internal/wasm/lib/double.dart
index 03705070c45..c0d0255f4f3 100644
--- a/sdk/lib/_internal/wasm/lib/double.dart
+++ b/sdk/lib/_internal/wasm/lib/double.dart
@@ -60,9 +60,6 @@ final class _BoxedDouble extends double {
   /// Dummy factory to silence error about missing superclass constructor.
   external factory _BoxedDouble();
 
-  @override
-  Type get runtimeType => double;
-
   static const int _mantissaBits = 52;
   static const int _exponentBits = 11;
   static const int _exponentBias = 1023;
diff --git a/sdk/lib/_internal/wasm/lib/errors_patch.dart b/sdk/lib/_internal/wasm/lib/errors_patch.dart
index ba30d82f0ff..af07caa106b 100644
--- a/sdk/lib/_internal/wasm/lib/errors_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/errors_patch.dart
@@ -7,9 +7,7 @@ part of 'core_patch.dart';
 @patch
 class Error {
   @patch
-  static String _objectToString(Object object) {
-    return "Instance of '${object._runtimeType}'";
-  }
+  static String _objectToString(Object object) => Object._toString(object);
 
   @patch
   static String _stringToSafeString(String string) {
diff --git a/sdk/lib/_internal/wasm/lib/int.dart b/sdk/lib/_internal/wasm/lib/int.dart
index 359361af3ed..c5543fb2a54 100644
--- a/sdk/lib/_internal/wasm/lib/int.dart
+++ b/sdk/lib/_internal/wasm/lib/int.dart
@@ -34,9 +34,6 @@ final class _BoxedInt extends int {
   /// Dummy factory to silence error about missing superclass constructor.
   external factory _BoxedInt();
 
-  @override
-  Type get runtimeType => int;
-
   external num operator +(num other);
   external num operator -(num other);
   external num operator *(num other);
diff --git a/sdk/lib/_internal/wasm/lib/object_patch.dart b/sdk/lib/_internal/wasm/lib/object_patch.dart
index 706467d9223..e971efb5132 100644
--- a/sdk/lib/_internal/wasm/lib/object_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/object_patch.dart
@@ -8,11 +8,6 @@ part of "core_patch.dart";
 external int _getHash(Object obj);
 external void _setHash(Object obj, int hash);
 
-external _Type _getInterfaceTypeRuntimeType(
-    Object object, List<Type> typeArguments);
-
-external _Type _getFunctionTypeRuntimeType(Object object);
-
 @patch
 class Object {
   @patch
@@ -43,24 +38,21 @@ class Object {
   /// which return their type arguments.
   List<_Type> get _typeArguments => const [];
 
-  /// We use [_runtimeType] for internal type testing, because objects can
-  /// override [runtimeType].
+  // An instance member needs a call from Dart code to be properly included in
+  // the dispatch table. Hence we use an inlined static wrapper as entry point.
+  @pragma("wasm:entry-point")
+  @pragma("wasm:prefer-inline")
+  static List<_Type> _getTypeArguments(Object object) => object._typeArguments;
+
   @patch
   external Type get runtimeType;
 
-  @pragma("wasm:entry-point")
-  _Type get _runtimeType {
-    if (ClassID.getID(this) == ClassID.cid_Closure) {
-      return _getFunctionTypeRuntimeType(this);
-    } else {
-      return _getInterfaceTypeRuntimeType(this, _typeArguments);
-    }
-  }
-
   @patch
   String toString() => _toString(this);
   // A statically dispatched version of Object.toString.
-  static String _toString(obj) => "Instance of '${obj.runtimeType}'";
+  static String _toString(Object obj) {
+    return "Instance of '${_getMasqueradedRuntimeType(obj)}'";
+  }
 
   @patch
   @pragma("wasm:entry-point")
diff --git a/sdk/lib/_internal/wasm/lib/record_patch.dart b/sdk/lib/_internal/wasm/lib/record_patch.dart
index 7b784746be0..c33283133e2 100644
--- a/sdk/lib/_internal/wasm/lib/record_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/record_patch.dart
@@ -7,4 +7,13 @@ part of "core_patch.dart";
 // `entry-point` needed to make sure the class will be in the class hierarchy
 // in programs without records.
 @pragma('wasm:entry-point')
-abstract class Record {}
+abstract class Record {
+  _Type get _recordRuntimeType;
+
+  // An instance member needs a call from Dart code to be properly included in
+  // the dispatch table. Hence we use an inlined static wrapper as entry point.
+  @pragma("wasm:entry-point")
+  @pragma("wasm:prefer-inline")
+  static _Type _getRecordRuntimeType(Record record) =>
+      record._recordRuntimeType;
+}
diff --git a/sdk/lib/_internal/wasm/lib/simd_patch.dart b/sdk/lib/_internal/wasm/lib/simd_patch.dart
index bba4c3700eb..ca7515f055c 100644
--- a/sdk/lib/_internal/wasm/lib/simd_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/simd_patch.dart
@@ -177,9 +177,6 @@ final class _NaiveFloat32x4List extends Object
 
   _NaiveFloat32x4List(int length) : _storage = Float32List(length * 4);
 
-  @override
-  Type get runtimeType => Float32x4List;
-
   _NaiveFloat32x4List._externalStorage(this._storage);
 
   _NaiveFloat32x4List._slowFromList(List<Float32x4> list)
@@ -243,9 +240,6 @@ final class _NaiveFloat64x2List extends Object
 
   _NaiveFloat64x2List(int length) : _storage = Float64List(length * 2);
 
-  @override
-  Type get runtimeType => Float64x2List;
-
   _NaiveFloat64x2List._externalStorage(this._storage);
 
   _NaiveFloat64x2List._slowFromList(List<Float64x2> list)
@@ -338,9 +332,6 @@ final class _NaiveFloat32x4 implements Float32x4 {
 
   _NaiveFloat32x4._truncated(this.x, this.y, this.z, this.w);
 
-  @override
-  Type get runtimeType => Float32x4List;
-
   @override
   String toString() {
     return '[${x.toStringAsFixed(6)}, '
diff --git a/sdk/lib/_internal/wasm/lib/string_patch.dart b/sdk/lib/_internal/wasm/lib/string_patch.dart
index 810f177f8fb..4fc78b0c42b 100644
--- a/sdk/lib/_internal/wasm/lib/string_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/string_patch.dart
@@ -95,9 +95,6 @@ abstract final class _StringBase implements String {
 
   _StringBase._();
 
-  @override
-  Type get runtimeType => String;
-
   int get hashCode {
     int hash = _getHash(this);
     if (hash != 0) return hash;
diff --git a/sdk/lib/_internal/wasm/lib/type.dart b/sdk/lib/_internal/wasm/lib/type.dart
index 2dd1c5f16b0..75aeae564ec 100644
--- a/sdk/lib/_internal/wasm/lib/type.dart
+++ b/sdk/lib/_internal/wasm/lib/type.dart
@@ -1026,7 +1026,8 @@ _TypeUniverse _typeUniverse = _TypeUniverse.create();
 
 @pragma("wasm:entry-point")
 bool _isSubtype(Object? s, _Type t) {
-  return _typeUniverse.isSubtype(s._runtimeType, null, t, null);
+  return _typeUniverse.isSubtype(
+      _getActualRuntimeTypeNullable(s), null, t, null);
 }
 
 @pragma("wasm:entry-point")
@@ -1166,3 +1167,17 @@ void _checkClosureType(_FunctionType functionType, List<_Type> typeArguments,
     }
   }
 }
+
+@pragma("wasm:entry-point")
+external _Type _getActualRuntimeType(Object object);
+
+@pragma("wasm:prefer-inline")
+_Type _getActualRuntimeTypeNullable(Object? object) =>
+    object == null ? const _NullType() : _getActualRuntimeType(object);
+
+@pragma("wasm:entry-point")
+external _Type _getMasqueradedRuntimeType(Object object);
+
+@pragma("wasm:prefer-inline")
+_Type _getMasqueradedRuntimeTypeNullable(Object? object) =>
+    object == null ? const _NullType() : _getMasqueradedRuntimeType(object);
diff --git a/sdk/lib/_internal/wasm/lib/typed_data_patch.dart b/sdk/lib/_internal/wasm/lib/typed_data_patch.dart
index 900091623de..9794aa4d809 100644
--- a/sdk/lib/_internal/wasm/lib/typed_data_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/typed_data_patch.dart
@@ -100,69 +100,3 @@ abstract class _TypedList extends _TypedListBase {
     data.setFloat64(offsetInBytes + 1 * 8, value.y, Endian.host);
   }
 }
-
-@patch
-class _Int8List {
-  @override
-  Type get runtimeType => Int8List;
-}
-
-@patch
-class _Uint8List {
-  @override
-  Type get runtimeType => Uint8List;
-}
-
-@patch
-class _Uint8ClampedList {
-  @override
-  Type get runtimeType => Uint8ClampedList;
-}
-
-@patch
-class _Int16List {
-  @override
-  Type get runtimeType => Int16List;
-}
-
-@patch
-class _Uint16List {
-  @override
-  Type get runtimeType => Uint16List;
-}
-
-@patch
-class _Int32List {
-  @override
-  Type get runtimeType => Int32List;
-}
-
-@patch
-class _Uint32List {
-  @override
-  Type get runtimeType => Uint32List;
-}
-
-@patch
-class _Int64List {
-  @override
-  Type get runtimeType => Int64List;
-}
-
-@patch
-class _Uint64List {
-  @override
-  Type get runtimeType => Uint64List;
-}
-
-@patch
-class _Float32List {
-  @override
-  Type get runtimeType => Float32List;
-}
-
-@patch
-class _Float64List {
-  @override
-  Type get runtimeType => Float64List;
-}
diff --git a/tests/language/records/simple/overridden_runtimetype_test.dart b/tests/language/records/simple/overridden_runtimetype_test.dart
new file mode 100644
index 00000000000..108f636d53a
--- /dev/null
+++ b/tests/language/records/simple/overridden_runtimetype_test.dart
@@ -0,0 +1,40 @@
+// Copyright (c) 2023, 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.
+
+// SharedOptions=--enable-experiment=records
+
+import "package:expect/expect.dart";
+
+class A {
+  @override
+  Type get runtimeType => B;
+}
+
+class B extends A {
+  @override
+  Type get runtimeType => A;
+}
+
+Type typeObject<T>() => T;
+
+main() {
+  final a = A();
+  final b = B();
+
+  Expect.isTrue(a is A);
+  Expect.isFalse(a is B);
+  Expect.isTrue(b is A);
+  Expect.isTrue(b is B);
+
+  Expect.isTrue((a,) is (A,));
+  Expect.isFalse((a,) is (B,));
+  Expect.isTrue((b,) is (A,));
+  Expect.isTrue((b,) is (B,));
+
+  Expect.equals(typeObject<B>(), a.runtimeType);
+  Expect.equals(typeObject<A>(), b.runtimeType);
+
+  Expect.equals(typeObject<(A,)>(), (a,).runtimeType);
+  Expect.equals(typeObject<(B,)>(), (b,).runtimeType);
+}