diff --git a/mobx_codegen/CHANGELOG.md b/mobx_codegen/CHANGELOG.md
index bfa7313c..e1fcfd20 100644
--- a/mobx_codegen/CHANGELOG.md
+++ b/mobx_codegen/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.6.2
+
+- Fixes [error with code generation when file has unnamed extension](https://github.com/mobxjs/mobx.dart/issues/1010) by [@amondnet](https://github.com/amondnet) in [#1020](https://github.com/mobxjs/mobx.dart/pull/1020) 
+
 ## 2.6.1
 
 - Upgrading packages and sdk
diff --git a/mobx_codegen/lib/src/template/method_override.dart b/mobx_codegen/lib/src/template/method_override.dart
index d07e45ca..1a31e6f2 100644
--- a/mobx_codegen/lib/src/template/method_override.dart
+++ b/mobx_codegen/lib/src/template/method_override.dart
@@ -43,7 +43,7 @@ class MethodOverrideTemplate {
 
   late String name;
   late String returnType;
-  late SurroundedCommaList<String> returnTypeArgs;
+  late SurroundedCommaList<String?> returnTypeArgs;
 
   late SurroundedCommaList<TypeParamTemplate> _typeParams;
   late SurroundedCommaList<String> _typeArgs;
diff --git a/mobx_codegen/lib/src/type_names.dart b/mobx_codegen/lib/src/type_names.dart
index 4992928c..f5211651 100644
--- a/mobx_codegen/lib/src/type_names.dart
+++ b/mobx_codegen/lib/src/type_names.dart
@@ -22,14 +22,14 @@ class LibraryScopedNameFinder {
 
   final LibraryElement library;
 
-  final Map<Element, String> _namesByElement = {};
+  final Map<Element, String?> _namesByElement = {};
 
-  Map<Element, String> get namesByElement {
+  Map<Element, String?> get namesByElement {
     // Add all of this library's type-defining elements to the name map
     final libraryElements =
         library.topLevelElements.whereType<TypeDefiningElement>();
     for (final element in libraryElements) {
-      _namesByElement[element] = element.name!;
+      _namesByElement[element] = element.name;
     }
 
     // Reverse each import's export namespace so we can map elements to their
@@ -58,14 +58,14 @@ class LibraryScopedNameFinder {
   String findReturnTypeName(FunctionTypedElement executable) =>
       _getDartTypeName(executable.returnType);
 
-  List<String> findReturnTypeArgumentTypeNames(ExecutableElement executable) {
+  List<String?> findReturnTypeArgumentTypeNames(ExecutableElement executable) {
     final returnType = executable.returnType;
     return returnType is ParameterizedType
         ? returnType.typeArguments.map(_getDartTypeName).toList()
         : [];
   }
 
-  String findTypeParameterBoundsTypeName(TypeParameterElement typeParameter) {
+  String? findTypeParameterBoundsTypeName(TypeParameterElement typeParameter) {
     assert(typeParameter.bound != null);
     return _getDartTypeName(typeParameter.bound!);
   }
@@ -88,7 +88,6 @@ class LibraryScopedNameFinder {
         typeElement == null ||
             // This is a bare type param, like "T"
             type is TypeParameterType) {
-      // ignore: deprecated_member_use_from_same_package
       return type.getDisplayString();
     }
 
diff --git a/mobx_codegen/lib/version.dart b/mobx_codegen/lib/version.dart
index 2bae6d5c..99454540 100644
--- a/mobx_codegen/lib/version.dart
+++ b/mobx_codegen/lib/version.dart
@@ -1,4 +1,4 @@
 // Generated via set_version.dart. !!!DO NOT MODIFY BY HAND!!!
 
 /// The current version as per `pubspec.yaml`.
-const version = '2.6.1';
+const version = '2.6.2';
diff --git a/mobx_codegen/pubspec.yaml b/mobx_codegen/pubspec.yaml
index a1dc4479..c673423b 100644
--- a/mobx_codegen/pubspec.yaml
+++ b/mobx_codegen/pubspec.yaml
@@ -1,6 +1,6 @@
 name: mobx_codegen
 description: Code generator for MobX that adds support for annotating your code with @observable, @computed, @action and also creating Store classes.
-version: 2.6.1
+version: 2.6.2
 
 repository: https://github.com/mobxjs/mobx.dart
 issue_tracker: https://github.com/mobxjs/mobx.dart/issues
diff --git a/mobx_codegen/test/data/with_extension_input.dart b/mobx_codegen/test/data/with_extension_input.dart
new file mode 100644
index 00000000..5618a8ee
--- /dev/null
+++ b/mobx_codegen/test/data/with_extension_input.dart
@@ -0,0 +1,15 @@
+library generator_sample;
+
+import 'package:mobx/mobx.dart';
+
+part 'store_with_extension.g.dart';
+
+// ignore: library_private_types_in_public_api
+class Foo = _Foo with _$Foo;
+
+abstract class _Foo with Store {
+  @observable
+  late String name;
+}
+
+extension on int {}
\ No newline at end of file
diff --git a/mobx_codegen/test/data/with_extension_output.dart b/mobx_codegen/test/data/with_extension_output.dart
new file mode 100644
index 00000000..573e5ba0
--- /dev/null
+++ b/mobx_codegen/test/data/with_extension_output.dart
@@ -0,0 +1,36 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'store_with_extension.dart';
+
+// **************************************************************************
+// StoreGenerator
+// **************************************************************************
+
+// ignore_for_file: non_constant_identifier_names, unnecessary_brace_in_string_interps, unnecessary_lambdas, prefer_expression_function_bodies, lines_longer_than_80_chars, avoid_as, avoid_annotating_with_dynamic, no_leading_underscores_for_local_identifiers
+
+mixin _$Foo on _Foo, Store {
+  late final _$nameAtom = Atom(name: '_Foo.name', context: context);
+
+  @override
+  String get name {
+    _$nameAtom.reportRead();
+    return super.name;
+  }
+
+  bool _nameIsInitialized = false;
+
+  @override
+  set name(String value) {
+    _$nameAtom.reportWrite(value, _nameIsInitialized ? super.name : null, () {
+      super.name = value;
+      _nameIsInitialized = true;
+    });
+  }
+
+  @override
+  String toString() {
+    return '''
+name: ${name}
+    ''';
+  }
+}
\ No newline at end of file
diff --git a/mobx_codegen/test/mobx_codegen_test.dart b/mobx_codegen/test/mobx_codegen_test.dart
index 87222fcf..6e351629 100644
--- a/mobx_codegen/test/mobx_codegen_test.dart
+++ b/mobx_codegen/test/mobx_codegen_test.dart
@@ -59,6 +59,11 @@ void main() {
           './data/valid_keep_alive_computed_output.dart');
     });
 
+    test('generates for a class with extension', () async {
+      await compareFiles('./data/with_extension_input.dart',
+          './data/with_extension_output.dart');
+    });
+
     createTests([
       const TestInfo(
           description: 'invalid output is handled',