diff --git a/LanguageFeatures/Extension-methods/syntax_name_t01.dart b/LanguageFeatures/Extension-methods/syntax_name_t01.dart
index c58ac78f7f..ddaf865501 100644
--- a/LanguageFeatures/Extension-methods/syntax_name_t01.dart
+++ b/LanguageFeatures/Extension-methods/syntax_name_t01.dart
@@ -2,28 +2,21 @@
 // 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.
 
-/// @assertion an extension declaration is a top-level declaration with a grammar
-/// similar to:
+/// @assertion an extension declaration is a top-level declaration with a
+/// grammar similar to:
 /// <extension> ::=
 ///   `extension' <identifier>? <typeParameters>? `on' <type> `?'? `{'
 ///     memberDeclaration*
 ///   `}'
 /// Such a declaration introduces its name (the identifier) into the surrounding
 /// scope. The name does not denote a type, but it can be used to denote the
-/// extension itself in various places. The name can be hidden or shown in import
-/// or export declarations.
+/// extension itself in various places. The name can be hidden or shown in
+/// import export declarations.
 ///
 /// @description Check that the name does not denote a type
 /// @author sgrekhov@unipro.ru
 
-
-
-extension MyFancyList<T> on List<T> {
-  int get doubleLength => this.length * 2;
-  List<T> operator-() => this.reversed.toList();
-  List<List<T>> split(int at) => <List<T>>[this.sublist(0, at), this.sublist(at)];
-  static String get className => "List";
-}
+extension MyFancyList<T> on List<T> {}
 
 main() {
   MyFancyList<String> list = ["Lily", "was", "here"];
diff --git a/LanguageFeatures/Extension-methods/syntax_name_t02.dart b/LanguageFeatures/Extension-methods/syntax_name_t02.dart
index 836295f56c..4c9e2b53fc 100644
--- a/LanguageFeatures/Extension-methods/syntax_name_t02.dart
+++ b/LanguageFeatures/Extension-methods/syntax_name_t02.dart
@@ -2,22 +2,20 @@
 // 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.
 
-/// @assertion an extension declaration is a top-level declaration with a grammar
-/// similar to:
+/// @assertion an extension declaration is a top-level declaration with a
+/// grammar similar to:
 /// <extension> ::=
 ///   `extension' <identifier>? <typeParameters>? `on' <type> `?'? `{'
 ///     memberDeclaration*
 ///   `}'
 /// Such a declaration introduces its name (the identifier) into the surrounding
 /// scope. The name does not denote a type, but it can be used to denote the
-/// extension itself in various places. The name can be hidden or shown in import
-/// or export declarations.
+/// extension itself in various places. The name can be hidden or shown in
+/// import export declarations.
 ///
 /// @description Check that the name does not denote a type
 /// @author sgrekhov@unipro.ru
 
-
-
 import "my_fancy_list_lib.dart";
 
 main() {
diff --git a/LanguageFeatures/Extension-methods/syntax_name_t03.dart b/LanguageFeatures/Extension-methods/syntax_name_t03.dart
index 8593c8efb1..339c28edef 100644
--- a/LanguageFeatures/Extension-methods/syntax_name_t03.dart
+++ b/LanguageFeatures/Extension-methods/syntax_name_t03.dart
@@ -2,23 +2,21 @@
 // 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.
 
-/// @assertion an extension declaration is a top-level declaration with a grammar
-/// similar to:
+/// @assertion an extension declaration is a top-level declaration with a
+/// grammar similar to:
 /// <extension> ::=
 ///   `extension' <identifier>? <typeParameters>? `on' <type> `?'? `{'
 ///     memberDeclaration*
 ///   `}'
 /// Such a declaration introduces its name (the identifier) into the surrounding
 /// scope. The name does not denote a type, but it can be used to denote the
-/// extension itself in various places. The name can be hidden or shown in import
-/// or export declarations.
+/// extension itself in various places. The name can be hidden or shown in
+/// import export declarations.
 ///
 /// @description Check that the name can be hidden or shown in import or export
 /// declarations.
 /// @author sgrekhov@unipro.ru
 
-
-
 import "my_fancy_list_lib.dart" hide MyFancyList;
 
 main() {
diff --git a/LanguageFeatures/Extension-methods/syntax_name_t04.dart b/LanguageFeatures/Extension-methods/syntax_name_t04.dart
index 8bf1dd961f..7cf78e6077 100644
--- a/LanguageFeatures/Extension-methods/syntax_name_t04.dart
+++ b/LanguageFeatures/Extension-methods/syntax_name_t04.dart
@@ -2,23 +2,21 @@
 // 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.
 
-/// @assertion an extension declaration is a top-level declaration with a grammar
-/// similar to:
+/// @assertion an extension declaration is a top-level declaration with a
+/// grammar similar to:
 /// <extension> ::=
 ///   `extension' <identifier>? <typeParameters>? `on' <type> `?'? `{'
 ///     memberDeclaration*
 ///   `}'
 /// Such a declaration introduces its name (the identifier) into the surrounding
 /// scope. The name does not denote a type, but it can be used to denote the
-/// extension itself in various places. The name can be hidden or shown in import
-/// or export declarations.
+/// extension itself in various places. The name can be hidden or shown in
+/// import export declarations.
 ///
 /// @description Check that the name can be hidden or shown in import or export
 /// declarations.
 /// @author sgrekhov@unipro.ru
 
-
-
 import "../../Utils/expect.dart";
 import "my_fancy_list_lib.dart" show MyFancyList;
 
diff --git a/LanguageFeatures/Extension-methods/syntax_name_t05.dart b/LanguageFeatures/Extension-methods/syntax_name_t05.dart
new file mode 100644
index 0000000000..102651c976
--- /dev/null
+++ b/LanguageFeatures/Extension-methods/syntax_name_t05.dart
@@ -0,0 +1,30 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion an extension declaration is a top-level declaration with a
+/// grammar similar to:
+/// <extension> ::=
+///   `extension' <identifier>? <typeParameters>? `on' <type> `?'? `{'
+///     memberDeclaration*
+///   `}'
+/// Such a declaration introduces its name (the identifier) into the surrounding
+/// scope. The name does not denote a type, but it can be used to denote the
+/// extension itself in various places. The name can be hidden or shown in
+/// import export declarations.
+///
+/// @description Check that it is a compile-time error to create a type alias
+/// for an extension
+/// @author sgrekhov22@gmail.com
+
+class A {}
+extension Ext on A {}
+
+typedef ExtAlias = Ext;
+//                 ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(A);
+}