diff --git a/pkg/analyzer/test/src/diagnostics/ffi_leaf_call_must_not_use_handle_test.dart b/pkg/analyzer/test/src/diagnostics/ffi_leaf_call_must_not_use_handle_test.dart
index c0deefae39f..1420d127647 100644
--- a/pkg/analyzer/test/src/diagnostics/ffi_leaf_call_must_not_use_handle_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/ffi_leaf_call_must_not_use_handle_test.dart
@@ -50,14 +50,14 @@ doThings() {
     await assertErrorsInCode(r'''
 import 'dart:ffi';
 
-class NativeFieldWrapperClass1 {}
+base class NativeFieldWrapperClass1 {}
 
-class A extends NativeFieldWrapperClass1 {
+base class A extends NativeFieldWrapperClass1 {
   @FfiNative<Handle Function(Pointer<Void>)>('foo', isLeaf:true)
   external Object get foo;
 }
 ''', [
-      error(FfiCode.LEAF_CALL_MUST_NOT_RETURN_HANDLE, 100, 89),
+      error(FfiCode.LEAF_CALL_MUST_NOT_RETURN_HANDLE, 110, 89),
     ]);
   }
 
diff --git a/pkg/analyzer/test/src/diagnostics/ffi_native_test.dart b/pkg/analyzer/test/src/diagnostics/ffi_native_test.dart
index 79cf773ea97..91c04f79e04 100644
--- a/pkg/analyzer/test/src/diagnostics/ffi_native_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/ffi_native_test.dart
@@ -21,9 +21,9 @@ class FfiNativeTest extends PubPackageResolutionTest {
     await assertErrorsInCode(r'''
 import 'dart:ffi';
 
-class NativeFieldWrapperClass1 {}
+base class NativeFieldWrapperClass1 {}
 
-class Paragraph extends NativeFieldWrapperClass1 {
+base class Paragraph extends NativeFieldWrapperClass1 {
   @FfiNative<Double Function(Pointer<Void>)>('Paragraph::ideographicBaseline', isLeaf: true)
   external double get ideographicBaseline;
 
@@ -190,9 +190,9 @@ class NativeTest extends PubPackageResolutionTest {
     await assertNoErrorsInCode(r'''
 import 'dart:ffi';
 
-class NativeFieldWrapperClass1 {}
+base class NativeFieldWrapperClass1 {}
 
-class Paragraph extends NativeFieldWrapperClass1 {
+base class Paragraph extends NativeFieldWrapperClass1 {
   @Native<Double Function(Pointer<Void>)>(isLeaf: true)
   external double get ideographicBaseline;
 
diff --git a/runtime/tests/vm/dart/isolates/fast_object_copy_test.dart b/runtime/tests/vm/dart/isolates/fast_object_copy_test.dart
index 955c5b230b0..0809c7fff10 100644
--- a/runtime/tests/vm/dart/isolates/fast_object_copy_test.dart
+++ b/runtime/tests/vm/dart/isolates/fast_object_copy_test.dart
@@ -26,7 +26,7 @@ import 'dart:typed_data';
 
 import 'package:expect/expect.dart';
 
-class ClassWithNativeFields extends NativeFieldWrapperClass1 {
+base class ClassWithNativeFields extends NativeFieldWrapperClass1 {
   void m() {}
 }
 
diff --git a/runtime/tests/vm/dart/isolates/send_unsupported_objects_test.dart b/runtime/tests/vm/dart/isolates/send_unsupported_objects_test.dart
index d286460d4aa..8890b8a08ad 100644
--- a/runtime/tests/vm/dart/isolates/send_unsupported_objects_test.dart
+++ b/runtime/tests/vm/dart/isolates/send_unsupported_objects_test.dart
@@ -20,7 +20,7 @@ class Bar {
   Foo foo = Foo();
 }
 
-class NativeClass extends NativeFieldWrapperClass1 {}
+base class NativeClass extends NativeFieldWrapperClass1 {}
 
 class Baz {
   @pragma('vm:entry-point') // prevent tree-shaking of the field.
diff --git a/runtime/tests/vm/dart/sendandexit_test.dart b/runtime/tests/vm/dart/sendandexit_test.dart
index bbcb3b076ad..8c00a9c8f59 100644
--- a/runtime/tests/vm/dart/sendandexit_test.dart
+++ b/runtime/tests/vm/dart/sendandexit_test.dart
@@ -26,7 +26,7 @@ spawnWorker(worker, data) async {
   return await completer.future;
 }
 
-class NativeWrapperClass extends NativeFieldWrapperClass1 {}
+base class NativeWrapperClass extends NativeFieldWrapperClass1 {}
 
 verifyCantSendNative() async {
   final receivePort = ReceivePort();
diff --git a/runtime/vm/benchmark_test.cc b/runtime/vm/benchmark_test.cc
index f6bce67f332..e99ebd14f82 100644
--- a/runtime/vm/benchmark_test.cc
+++ b/runtime/vm/benchmark_test.cc
@@ -168,7 +168,7 @@ BENCHMARK(UseDartApi) {
   const char* kScriptChars = R"(
 import 'dart:nativewrappers';
 
-class Class extends NativeFieldWrapperClass1 {
+base class Class extends NativeFieldWrapperClass1 {
   @pragma("vm:external-name", "init")
   external void init();
   @pragma("vm:external-name", "method")
diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
index 2c7c6023070..6df4c750e48 100644
--- a/runtime/vm/dart_api_impl_test.cc
+++ b/runtime/vm/dart_api_impl_test.cc
@@ -4601,7 +4601,7 @@ void FUNCTION_NAME(ExampleResource_Dispose)(Dart_NativeArguments native_args) {
 TEST_CASE(DartAPI_WeakPersistentHandleUpdateSize) {
   const char* kScriptChars = R"(
     import "dart:nativewrappers";
-    class ExampleResource extends NativeFieldWrapperClass1 {
+    base class ExampleResource extends NativeFieldWrapperClass1 {
       ExampleResource() { _allocate(); }
       @pragma("vm:external-name", "ExampleResource_Allocate")
       external void _allocate();
@@ -4660,7 +4660,7 @@ TEST_CASE(DartAPI_NativeFieldAccess) {
   const char* kScriptChars = R"(
     import 'dart:ffi';
     import 'dart:nativewrappers';
-    class SecretKeeper extends NativeFieldWrapperClass1 {
+    base class SecretKeeper extends NativeFieldWrapperClass1 {
       SecretKeeper(int secret) { _keepSecret(secret); }
       @pragma("vm:external-name", "SecretKeeper_KeepSecret")
       external void _keepSecret(int secret);
@@ -4694,7 +4694,7 @@ TEST_CASE(DartAPI_NativeFieldAccess_Throws) {
   const char* kScriptChars = R"(
     import 'dart:ffi';
     import 'dart:nativewrappers';
-    class ForgetfulSecretKeeper extends NativeFieldWrapperClass1 {
+    base class ForgetfulSecretKeeper extends NativeFieldWrapperClass1 {
       ForgetfulSecretKeeper(int secret) { /* Forget to init. native field. */ }
     }
     // Argument auto-conversion will wrap `o` in `_getNativeField()`.
@@ -5699,7 +5699,8 @@ TEST_CASE(DartAPI_InjectNativeFields3) {
   auto kScriptChars = Utils::CStringUniquePtr(
       OS::SCreate(nullptr,
                   "import 'dart:nativewrappers';"
-                  "class NativeFields extends NativeFieldWrapperClass2 {\n"
+                  "final class NativeFields "
+                  "extends NativeFieldWrapperClass2 {\n"
                   "  NativeFields(int i, int j) : fld1 = i, fld2 = j {}\n"
                   "  int fld1;\n"
                   "  final int fld2;\n"
@@ -5843,7 +5844,7 @@ TEST_CASE(DartAPI_TestNativeFieldsAccess) {
       OS::SCreate(
           nullptr, R"(
           import 'dart:nativewrappers';
-          class NativeFields extends NativeFieldWrapperClass2 {
+          base class NativeFields extends NativeFieldWrapperClass2 {
             NativeFields(int i, int j) : fld1 = i, fld2 = j {}
             int fld1;
             final int fld2;
@@ -5883,11 +5884,11 @@ TEST_CASE(DartAPI_TestNativeFieldsAccess) {
 TEST_CASE(DartAPI_InjectNativeFieldsSuperClass) {
   const char* kScriptChars =
       "import 'dart:nativewrappers';"
-      "class NativeFieldsSuper extends NativeFieldWrapperClass1 {\n"
+      "base class NativeFieldsSuper extends NativeFieldWrapperClass1 {\n"
       "  NativeFieldsSuper() : fld1 = 42 {}\n"
       "  int fld1;\n"
       "}\n"
-      "class NativeFields extends NativeFieldsSuper {\n"
+      "base class NativeFields extends NativeFieldsSuper {\n"
       "  fld() => fld1;\n"
       "}\n"
       "int testMain() {\n"
@@ -5990,7 +5991,8 @@ TEST_CASE(DartAPI_ImplicitNativeFieldAccess) {
   auto kScriptChars = Utils::CStringUniquePtr(
       OS::SCreate(nullptr,
                   "import 'dart:nativewrappers';"
-                  "class NativeFields extends NativeFieldWrapperClass4 {\n"
+                  "final class NativeFields extends "
+                  "NativeFieldWrapperClass4 {\n"
                   "  NativeFields(int i, int j) : fld1 = i, fld2 = j {}\n"
                   "  int%s fld0;\n"
                   "  int fld1;\n"
@@ -7424,7 +7426,7 @@ static Dart_NativeFunction native_args_lookup(Dart_Handle name,
 TEST_CASE(DartAPI_GetNativeArguments) {
   const char* kScriptChars = R"(
 import 'dart:nativewrappers';
-class MyObject extends NativeFieldWrapperClass2 {
+base class MyObject extends NativeFieldWrapperClass2 {
   @pragma("vm:external-name", "NativeArgument_Create")
   external static MyObject createObject();
   @pragma("vm:external-name", "NativeArgument_Access")
diff --git a/sdk/lib/_internal/vm/bin/directory_patch.dart b/sdk/lib/_internal/vm/bin/directory_patch.dart
index bf4b6ef7786..e0efabc10ea 100644
--- a/sdk/lib/_internal/vm/bin/directory_patch.dart
+++ b/sdk/lib/_internal/vm/bin/directory_patch.dart
@@ -49,7 +49,7 @@ class _AsyncDirectoryListerOps {
       new _AsyncDirectoryListerOpsImpl(pointer);
 }
 
-class _AsyncDirectoryListerOpsImpl extends NativeFieldWrapperClass1
+base class _AsyncDirectoryListerOpsImpl extends NativeFieldWrapperClass1
     implements _AsyncDirectoryListerOps {
   _AsyncDirectoryListerOpsImpl._();
 
diff --git a/sdk/lib/_internal/vm/bin/file_patch.dart b/sdk/lib/_internal/vm/bin/file_patch.dart
index 00d3ef8e4d2..383e95bf5e8 100644
--- a/sdk/lib/_internal/vm/bin/file_patch.dart
+++ b/sdk/lib/_internal/vm/bin/file_patch.dart
@@ -74,7 +74,7 @@ class _RandomAccessFileOps {
 }
 
 @pragma("vm:entry-point")
-class _RandomAccessFileOpsImpl extends NativeFieldWrapperClass1
+base class _RandomAccessFileOpsImpl extends NativeFieldWrapperClass1
     implements _RandomAccessFileOps {
   _RandomAccessFileOpsImpl._();
 
diff --git a/sdk/lib/_internal/vm/bin/filter_patch.dart b/sdk/lib/_internal/vm/bin/filter_patch.dart
index 79ed27d1edf..12eaee7232b 100644
--- a/sdk/lib/_internal/vm/bin/filter_patch.dart
+++ b/sdk/lib/_internal/vm/bin/filter_patch.dart
@@ -4,7 +4,8 @@
 
 part of "common_patch.dart";
 
-class _FilterImpl extends NativeFieldWrapperClass1 implements RawZLibFilter {
+base class _FilterImpl extends NativeFieldWrapperClass1
+    implements RawZLibFilter {
   @pragma("vm:external-name", "Filter_Process")
   external void process(List<int> data, int start, int end);
 
@@ -12,7 +13,7 @@ class _FilterImpl extends NativeFieldWrapperClass1 implements RawZLibFilter {
   external List<int>? processed({bool flush = true, bool end = false});
 }
 
-class _ZLibInflateFilter extends _FilterImpl {
+base class _ZLibInflateFilter extends _FilterImpl {
   _ZLibInflateFilter(int windowBits, List<int>? dictionary, bool raw) {
     _init(windowBits, dictionary, raw);
   }
@@ -20,7 +21,7 @@ class _ZLibInflateFilter extends _FilterImpl {
   external void _init(int windowBits, List<int>? dictionary, bool raw);
 }
 
-class _ZLibDeflateFilter extends _FilterImpl {
+base class _ZLibDeflateFilter extends _FilterImpl {
   _ZLibDeflateFilter(bool gzip, int level, int windowBits, int memLevel,
       int strategy, List<int>? dictionary, bool raw) {
     _init(gzip, level, windowBits, memLevel, strategy, dictionary, raw);
diff --git a/sdk/lib/_internal/vm/bin/namespace_patch.dart b/sdk/lib/_internal/vm/bin/namespace_patch.dart
index 97065dbced8..cf8b43aaf6f 100644
--- a/sdk/lib/_internal/vm/bin/namespace_patch.dart
+++ b/sdk/lib/_internal/vm/bin/namespace_patch.dart
@@ -5,7 +5,8 @@
 part of 'common_patch.dart';
 
 @pragma("vm:entry-point")
-class _NamespaceImpl extends NativeFieldWrapperClass1 implements _Namespace {
+base class _NamespaceImpl extends NativeFieldWrapperClass1
+    implements _Namespace {
   _NamespaceImpl._();
 
   @pragma("vm:external-name", "Namespace_Create")
diff --git a/sdk/lib/_internal/vm/bin/process_patch.dart b/sdk/lib/_internal/vm/bin/process_patch.dart
index 9dbd12da03a..196a44f5faf 100644
--- a/sdk/lib/_internal/vm/bin/process_patch.dart
+++ b/sdk/lib/_internal/vm/bin/process_patch.dart
@@ -213,9 +213,9 @@ class _ProcessStartStatus {
 
 // The NativeFieldWrapperClass1 can not be used with a mixin, due to missing
 // implicit constructor.
-class _ProcessImplNativeWrapper extends NativeFieldWrapperClass1 {}
+base class _ProcessImplNativeWrapper extends NativeFieldWrapperClass1 {}
 
-class _ProcessImpl extends _ProcessImplNativeWrapper implements _Process {
+base class _ProcessImpl extends _ProcessImplNativeWrapper implements _Process {
   static bool connectedResourceHandler = false;
 
   _ProcessImpl(
diff --git a/sdk/lib/_internal/vm/bin/secure_socket_patch.dart b/sdk/lib/_internal/vm/bin/secure_socket_patch.dart
index 9f6641dcd94..2a40fc4206a 100644
--- a/sdk/lib/_internal/vm/bin/secure_socket_patch.dart
+++ b/sdk/lib/_internal/vm/bin/secure_socket_patch.dart
@@ -60,7 +60,7 @@ class _SecureSocket extends _Socket implements SecureSocket {
  * native code can access the same data.
  */
 @pragma("vm:entry-point")
-class _SecureFilterImpl extends NativeFieldWrapperClass1
+base class _SecureFilterImpl extends NativeFieldWrapperClass1
     implements _SecureFilter {
   // Performance is improved if a full buffer of plaintext fits
   // in the encrypted buffer, when encrypted.
@@ -208,7 +208,7 @@ class SecurityContext {
   static bool get alpnSupported => true;
 }
 
-class _SecurityContext extends NativeFieldWrapperClass1
+base class _SecurityContext extends NativeFieldWrapperClass1
     implements SecurityContext {
   bool _allowLegacyUnsafeRenegotiation = false;
 
@@ -284,7 +284,7 @@ class _SecurityContext extends NativeFieldWrapperClass1
  * _X509CertificateImpl wraps an X509 certificate object held by the BoringSSL
  * library. It exposes the fields of the certificate object.
  */
-class _X509CertificateImpl extends NativeFieldWrapperClass1
+base class _X509CertificateImpl extends NativeFieldWrapperClass1
     implements X509Certificate {
   // The native field must be set manually on a new object, in native code.
   // This is done by WrappedX509Certificate in security_context.cc.
diff --git a/sdk/lib/_internal/vm/bin/socket_patch.dart b/sdk/lib/_internal/vm/bin/socket_patch.dart
index 5ae91a1b41a..e28bb75d646 100644
--- a/sdk/lib/_internal/vm/bin/socket_patch.dart
+++ b/sdk/lib/_internal/vm/bin/socket_patch.dart
@@ -370,14 +370,15 @@ class _NetworkInterface implements NetworkInterface {
 
 // The NativeFieldWrapperClass1 cannot be used with a mixin, due to missing
 // implicit constructor.
-class _NativeSocketNativeWrapper extends NativeFieldWrapperClass1 {}
+base class _NativeSocketNativeWrapper extends NativeFieldWrapperClass1 {}
 
 /// Returns error code that corresponds to EINPROGRESS OS error.
 @pragma("vm:external-name", "OSError_inProgressErrorCode")
 external int get _inProgressErrorCode;
 
 // The _NativeSocket class encapsulates an OS socket.
-class _NativeSocket extends _NativeSocketNativeWrapper with _ServiceObject {
+base class _NativeSocket extends _NativeSocketNativeWrapper
+    with _ServiceObject {
   // Bit flags used when communicating between the eventhandler and
   // dart code. The EVENT flags are used to indicate events of
   // interest when sending a message from dart code to the
diff --git a/sdk/lib/_internal/vm/bin/sync_socket_patch.dart b/sdk/lib/_internal/vm/bin/sync_socket_patch.dart
index 16fd08aff4b..bb0193969f8 100644
--- a/sdk/lib/_internal/vm/bin/sync_socket_patch.dart
+++ b/sdk/lib/_internal/vm/bin/sync_socket_patch.dart
@@ -45,10 +45,12 @@ class _RawSynchronousSocket implements RawSynchronousSocket {
 
 // The NativeFieldWrapperClass1 can not be used with a mixin, due to missing
 // implicit constructor.
-class _NativeSynchronousSocketNativeWrapper extends NativeFieldWrapperClass1 {}
+base class _NativeSynchronousSocketNativeWrapper
+    extends NativeFieldWrapperClass1 {}
 
 // The _NativeSynchronousSocket class encapsulates a synchronous OS socket.
-class _NativeSynchronousSocket extends _NativeSynchronousSocketNativeWrapper {
+base class _NativeSynchronousSocket
+    extends _NativeSynchronousSocketNativeWrapper {
   // Socket close state.
   bool isClosed = false;
   bool isClosedRead = false;
diff --git a/tests/ffi/ffi_native_test.dart b/tests/ffi/ffi_native_test.dart
index 808c70c89f8..99a22fee74d 100644
--- a/tests/ffi/ffi_native_test.dart
+++ b/tests/ffi/ffi_native_test.dart
@@ -16,7 +16,7 @@ class Classy {
   external void goodHasReceiverHandle(int v);
 }
 
-class NativeClassy extends NativeFieldWrapperClass1 {
+base class NativeClassy extends NativeFieldWrapperClass1 {
   @FfiNative<IntPtr Function(IntPtr)>('ReturnIntPtr')
   external static int returnIntPtrStatic(int x);
 
diff --git a/tests/ffi/vmspecific_ffi_native_test.dart b/tests/ffi/vmspecific_ffi_native_test.dart
index d8115eef4af..177192be9cc 100644
--- a/tests/ffi/vmspecific_ffi_native_test.dart
+++ b/tests/ffi/vmspecific_ffi_native_test.dart
@@ -48,7 +48,7 @@ class Classy {
 
 // For automatic transform of NativeFieldWrapperClass1 to Pointer.
 
-class ClassWithNativeField extends NativeFieldWrapperClass1 {
+base class ClassWithNativeField extends NativeFieldWrapperClass1 {
   ClassWithNativeField(int value) {
     setNativeInstanceField(this, 0, value);
   }
@@ -105,7 +105,7 @@ int setState(int value) {
   return 0;
 }
 
-class StateSetter extends NativeFieldWrapperClass1 {
+base class StateSetter extends NativeFieldWrapperClass1 {
   StateSetter(int value) {
     setNativeInstanceField(this, 0, 0);
     state = value;
diff --git a/tests/ffi/vmspecific_static_checks_ffinative_test.dart b/tests/ffi/vmspecific_static_checks_ffinative_test.dart
index 8038c09545c..0c207b26725 100644
--- a/tests/ffi/vmspecific_static_checks_ffinative_test.dart
+++ b/tests/ffi/vmspecific_static_checks_ffinative_test.dart
@@ -33,7 +33,7 @@ class Classy {
   external void badHasReceiverPointer(int v); //# 04: compile-time error
 }
 
-class NativeClassy extends NativeFieldWrapperClass1 {
+base class NativeClassy extends NativeFieldWrapperClass1 {
   // Error: Missing receiver in FfiNative annotation.
   @FfiNative<Void Function(IntPtr)>('doesntmatter') //# 05: compile-time error
   external void badMissingReceiver(int v); //# 05: compile-time error
diff --git a/tests/lib/isolate/native_wrapper_message_test.dart b/tests/lib/isolate/native_wrapper_message_test.dart
index fc901041bfb..24b7d005757 100644
--- a/tests/lib/isolate/native_wrapper_message_test.dart
+++ b/tests/lib/isolate/native_wrapper_message_test.dart
@@ -13,7 +13,7 @@ echo(msg) {
   reply.send('echoing ${data(1)}}');
 }
 
-class Test extends NativeFieldWrapperClass2 {
+base class Test extends NativeFieldWrapperClass2 {
   Test(this.i, this.j);
   int i, j;
 }
diff --git a/tests/web/wasm/ffi_native_test.dart b/tests/web/wasm/ffi_native_test.dart
index f3efb95405f..6a31195c2a2 100644
--- a/tests/web/wasm/ffi_native_test.dart
+++ b/tests/web/wasm/ffi_native_test.dart
@@ -93,7 +93,7 @@ external int incrementSize(int a);
 @Native<WChar Function(WChar)>()
 external int incrementWchar(int a);
 
-final class MyStruct extends Struct implements NativeFieldWrapperClass1 {
+final class MyStruct extends Struct {
   @Double()
   external double x;