diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb338ee0..42496d5d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,7 +3,7 @@
 * Require analyzer 5.2.0.
 * Fix nice mocks generation in mixed mode (generated code is pre null-safety,
   while mocked class is null-safe).
-* Require Dart >= 2.18.0.
+* Require Dart >= 2.17.0.
 * Support typedef-aliased classes in `@GenerateMocks` and `@GenerateNiceMocks`
 
 ## 5.3.2
diff --git a/analysis_options.yaml b/analysis_options.yaml
index 860c620e..0cfb93b3 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1,4 +1,5 @@
 include: package:lints/recommended.yaml
+
 analyzer:
   language:
     strict-casts: true
@@ -7,4 +8,4 @@ linter:
   rules:
     - comment_references
     - test_types_in_equals
-    - throw_in_finally
+    - throw_in_finally
\ No newline at end of file
diff --git a/lib/src/builder.dart b/lib/src/builder.dart
index 7ee303f2..71bbeb52 100644
--- a/lib/src/builder.dart
+++ b/lib/src/builder.dart
@@ -618,6 +618,11 @@ class _MockTargetGatherer {
       }
       final mixinInterfaceType =
           _determineDartType(typeToMixin, entryLib.typeProvider);
+      if (!mixinInterfaceType.interfaces.contains(type)) {
+        throw InvalidMockitoAnnotationException('The "mixingIn" type, '
+            '${typeToMixin.getDisplayString(withNullability: false)}, must '
+            'implement the class to mock, ${typeToMock.getDisplayString(withNullability: false)}');
+      }
       mixins.add(mixinInterfaceType);
     }
 
diff --git a/test/builder/custom_mocks_test.dart b/test/builder/custom_mocks_test.dart
index 81999230..71dc963f 100644
--- a/test/builder/custom_mocks_test.dart
+++ b/test/builder/custom_mocks_test.dart
@@ -415,29 +415,6 @@ void main() {
     );
   });
 
-  test('generates a mock class with a marker mixin', () async {
-    var mocksContent = await buildWithNonNullable({
-      ...annotationsAsset,
-      'foo|lib/foo.dart': '''
-        class Foo {}
-        class FooMarkerMixin {}
-        ''',
-      'foo|test/foo_test.dart': '''
-        import 'package:foo/foo.dart';
-        import 'package:mockito/annotations.dart';
-        @GenerateMocks([], customMocks: [
-          MockSpec<Foo>(mixingIn: [FooMarkerMixin])
-        ])
-        void main() {}
-        '''
-    });
-    expect(
-      mocksContent,
-      contains(
-          'class MockFoo extends _i1.Mock with _i2.FooMarkerMixin implements _i2.Foo {'),
-    );
-  });
-
   test(
       'generates a mock class which uses the old behavior of returning null on '
       'missing stubs', () async {
@@ -1238,6 +1215,27 @@ void main() {
     );
   });
 
+  test('throws when MockSpec mixes in a non-mixinable type', () async {
+    _expectBuilderThrows(
+      assets: {
+        ...annotationsAsset,
+        'foo|lib/foo.dart': dedent('''
+        class Foo {}
+        '''),
+        'foo|test/foo_test.dart': dedent('''
+        import 'package:mockito/annotations.dart';
+        import 'package:foo/foo.dart';
+        @GenerateMocks([], customMocks: [MockSpec<Foo>(mixingIn: [FooMixin])])
+        void main() {}
+
+        mixin FooMixin {}
+        '''),
+      },
+      message: contains(
+          'The "mixingIn" type, FooMixin, must implement the class to mock, Foo'),
+    );
+  });
+
   test('throws when type argument is unknown type', () async {
     _expectBuilderThrows(
       assets: {