diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart b/pkg/front_end/testcases/extensions/null_aware_set.dart
index 1a99a2ff9a3b..fc9731928f98 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart
@@ -2,7 +2,7 @@
 // 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.
 
-extension on Object {
+extension Foo on Object {
   set f(int x) {}
 }
 
diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline.expect b/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline.expect
index e1b7887af796..2f6c2f005ba4 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline.expect
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline.expect
@@ -1,4 +1,4 @@
-extension on Object {
+extension Foo on Object {
   set f(int x) {}
 }
 
diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline_modelled.expect
index e1b7887af796..2f6c2f005ba4 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline_modelled.expect
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart.textual_outline_modelled.expect
@@ -1,4 +1,4 @@
-extension on Object {
+extension Foo on Object {
   set f(int x) {}
 }
 
diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.expect b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.expect
index 4838f3015ced..fdecbf482165 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.expect
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.expect
@@ -2,10 +2,10 @@ library /*isNonNullableByDefault*/;
 import self as self;
 import "dart:core" as core;
 
-extension _extension#0 on core::Object {
-  set f = self::_extension#0|set#f;
+extension Foo on core::Object {
+  set f = self::Foo|set#f;
 }
-static method _extension#0|set#f(lowered final core::Object #this, core::int x) → void {}
+static method Foo|set#f(lowered final core::Object #this, core::int x) → void {}
 static method fun(core::String? s) → void {
-  let final core::String? #t1 = s in #t1 == null ?{void} null : self::_extension#0|set#f(#t1{core::String}, 1);
+  let final core::String? #t1 = s in #t1 == null ?{void} null : self::Foo|set#f(#t1{core::String}, 1);
 }
diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.modular.expect b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.modular.expect
index 4838f3015ced..fdecbf482165 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.modular.expect
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.modular.expect
@@ -2,10 +2,10 @@ library /*isNonNullableByDefault*/;
 import self as self;
 import "dart:core" as core;
 
-extension _extension#0 on core::Object {
-  set f = self::_extension#0|set#f;
+extension Foo on core::Object {
+  set f = self::Foo|set#f;
 }
-static method _extension#0|set#f(lowered final core::Object #this, core::int x) → void {}
+static method Foo|set#f(lowered final core::Object #this, core::int x) → void {}
 static method fun(core::String? s) → void {
-  let final core::String? #t1 = s in #t1 == null ?{void} null : self::_extension#0|set#f(#t1{core::String}, 1);
+  let final core::String? #t1 = s in #t1 == null ?{void} null : self::Foo|set#f(#t1{core::String}, 1);
 }
diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.outline.expect b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.outline.expect
index db9cc4ecd70c..cc402ab7ae2c 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.outline.expect
@@ -2,10 +2,10 @@ library /*isNonNullableByDefault*/;
 import self as self;
 import "dart:core" as core;
 
-extension _extension#0 on core::Object {
-  set f = self::_extension#0|set#f;
+extension Foo on core::Object {
+  set f = self::Foo|set#f;
 }
-static method _extension#0|set#f(lowered final core::Object #this, core::int x) → void
+static method Foo|set#f(lowered final core::Object #this, core::int x) → void
   ;
 static method fun(core::String? s) → void
   ;
diff --git a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.transformed.expect b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.transformed.expect
index 4838f3015ced..fdecbf482165 100644
--- a/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/extensions/null_aware_set.dart.weak.transformed.expect
@@ -2,10 +2,10 @@ library /*isNonNullableByDefault*/;
 import self as self;
 import "dart:core" as core;
 
-extension _extension#0 on core::Object {
-  set f = self::_extension#0|set#f;
+extension Foo on core::Object {
+  set f = self::Foo|set#f;
 }
-static method _extension#0|set#f(lowered final core::Object #this, core::int x) → void {}
+static method Foo|set#f(lowered final core::Object #this, core::int x) → void {}
 static method fun(core::String? s) → void {
-  let final core::String? #t1 = s in #t1 == null ?{void} null : self::_extension#0|set#f(#t1{core::String}, 1);
+  let final core::String? #t1 = s in #t1 == null ?{void} null : self::Foo|set#f(#t1{core::String}, 1);
 }