diff --git a/pkg/front_end/lib/src/fasta/kernel/hierarchy/members_builder.dart b/pkg/front_end/lib/src/fasta/kernel/hierarchy/members_builder.dart
index 13aac2c0381..0fc144c17b5 100644
--- a/pkg/front_end/lib/src/fasta/kernel/hierarchy/members_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/hierarchy/members_builder.dart
@@ -39,6 +39,7 @@ class ClassMembersBuilder implements ClassHierarchyMembers {
     _delayedChecks.clear();
     _delayedTypeComputations.clear();
     _delayedMemberComputations.clear();
+    extensionTypeDeclarationNodes.clear();
   }
 
   void registerDelayedTypeComputation(DelayedTypeComputation computation) {
diff --git a/pkg/front_end/testcases/incremental/extension_type.yaml b/pkg/front_end/testcases/incremental/extension_type.yaml
new file mode 100644
index 00000000000..64bdfc01ce0
--- /dev/null
+++ b/pkg/front_end/testcases/incremental/extension_type.yaml
@@ -0,0 +1,25 @@
+# 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.
+
+# Reproduce a leak.
+
+type: newworld
+worlds:
+  - entry: main.dart
+    noFullComponent: true
+    sources:
+      main.dart: |
+        extension type const _Foo._(int _foo) {
+          _Foo operator +(_Foo other) => throw "hello";
+        }
+    expectedLibraryCount: 1
+
+  - entry: main.dart
+    worldType: updated
+    expectInitializeFromDill: false
+    noFullComponent: true
+    invalidate:
+      - main.dart
+    expectedLibraryCount: 1
+    advancedInvalidation: bodiesOnly
diff --git a/pkg/front_end/testcases/incremental/extension_type.yaml.world.1.expect b/pkg/front_end/testcases/incremental/extension_type.yaml.world.1.expect
new file mode 100644
index 00000000000..37dafc9da9c
--- /dev/null
+++ b/pkg/front_end/testcases/incremental/extension_type.yaml.world.1.expect
@@ -0,0 +1,18 @@
+main = <No Member>;
+library from "org-dartlang-test:///main.dart" as main {
+
+  extension type _Foo(dart.core::int _foo) {
+    abstract extension-type-member representation-field get _foo() → dart.core::int;
+    operator + = main::_Foo|+;
+    constructor _ = main::_Foo|constructor#_;
+    constructor tearoff _ = main::_Foo|constructor#_#_#tearOff;
+  }
+  static extension-type-member method _Foo|constructor#_(dart.core::int _foo) → main::_Foo% /* erasure=dart.core::int, declared=! */ {
+    lowered final main::_Foo% /* erasure=dart.core::int, declared=! */ #this = _foo;
+    return #this;
+  }
+  static extension-type-member method _Foo|constructor#_#_#tearOff(dart.core::int _foo) → main::_Foo% /* erasure=dart.core::int, declared=! */
+    return main::_Foo|constructor#_(_foo);
+  static extension-type-member method _Foo|+(lowered final main::_Foo% /* erasure=dart.core::int, declared=! */ #this, main::_Foo% /* erasure=dart.core::int, declared=! */ other) → main::_Foo% /* erasure=dart.core::int, declared=! */
+    return throw "hello";
+}
diff --git a/pkg/front_end/testcases/incremental/extension_type.yaml.world.2.expect b/pkg/front_end/testcases/incremental/extension_type.yaml.world.2.expect
new file mode 100644
index 00000000000..37dafc9da9c
--- /dev/null
+++ b/pkg/front_end/testcases/incremental/extension_type.yaml.world.2.expect
@@ -0,0 +1,18 @@
+main = <No Member>;
+library from "org-dartlang-test:///main.dart" as main {
+
+  extension type _Foo(dart.core::int _foo) {
+    abstract extension-type-member representation-field get _foo() → dart.core::int;
+    operator + = main::_Foo|+;
+    constructor _ = main::_Foo|constructor#_;
+    constructor tearoff _ = main::_Foo|constructor#_#_#tearOff;
+  }
+  static extension-type-member method _Foo|constructor#_(dart.core::int _foo) → main::_Foo% /* erasure=dart.core::int, declared=! */ {
+    lowered final main::_Foo% /* erasure=dart.core::int, declared=! */ #this = _foo;
+    return #this;
+  }
+  static extension-type-member method _Foo|constructor#_#_#tearOff(dart.core::int _foo) → main::_Foo% /* erasure=dart.core::int, declared=! */
+    return main::_Foo|constructor#_(_foo);
+  static extension-type-member method _Foo|+(lowered final main::_Foo% /* erasure=dart.core::int, declared=! */ #this, main::_Foo% /* erasure=dart.core::int, declared=! */ other) → main::_Foo% /* erasure=dart.core::int, declared=! */
+    return throw "hello";
+}