diff --git a/packages/flutter/lib/fix_data.yaml b/packages/flutter/lib/fix_data.yaml
index 65b821ce28..55fe739e63 100644
--- a/packages/flutter/lib/fix_data.yaml
+++ b/packages/flutter/lib/fix_data.yaml
@@ -11,6 +11,26 @@
 version: 1
 transforms:
 
+  # Changes made in https://github.com/flutter/flutter/pull/15303
+  - title: 'Replace child with builder'
+    date: 2020-12-17
+    element:
+      uris: [ 'material.dart' ]
+      function: 'showDialog'
+    changes:
+      - kind: 'addParameter'
+        index: 0
+        name: 'builder'
+        style: optional_named
+        argumentValue:
+          expression: '(context) => {% widget %}'
+          requiredIf: "widget != ''"
+          variables:
+            widget:
+              kind: fragment
+              value: 'arguments[child]'
+      - kind: 'removeParameter'
+        name: 'child'
   # Changes made in https://github.com/flutter/flutter/pull/28602
   - title: 'Rename to fromMouseEvent'
     date: 2020-12-15
@@ -33,7 +53,6 @@ transforms:
       - kind: 'rename'
         newName: 'fromMouseEvent'
 
-
   # Changes made in https://github.com/flutter/flutter/pull/41859
   - title: 'Remove brightness'
     date: 2020-12-10
diff --git a/packages/flutter/lib/src/material/dialog.dart b/packages/flutter/lib/src/material/dialog.dart
index c9d406a832..2f931a564f 100644
--- a/packages/flutter/lib/src/material/dialog.dart
+++ b/packages/flutter/lib/src/material/dialog.dart
@@ -967,16 +967,8 @@ Future<T?> showDialog<T>({
   bool useSafeArea = true,
   bool useRootNavigator = true,
   RouteSettings? routeSettings,
-  @Deprecated(
-    'Instead of using the "child" argument, return the child from a closure '
-    'provided to the "builder" argument. This will ensure that the BuildContext '
-    'is appropriate for widgets built in the dialog. '
-    'This feature was deprecated after v0.2.3.'
-  )
-  Widget? child,
 }) {
-  assert(child == null || builder == null);
-  assert(child != null || builder != null);
+  assert(builder != null);
   assert(barrierDismissible != null);
   assert(useSafeArea != null);
   assert(useRootNavigator != null);
@@ -986,7 +978,7 @@ Future<T?> showDialog<T>({
   return showGeneralDialog(
     context: context,
     pageBuilder: (BuildContext buildContext, Animation<double> animation, Animation<double> secondaryAnimation) {
-      final Widget pageChild = child ?? Builder(builder: builder!);
+      final Widget pageChild = Builder(builder: builder!);
       Widget dialog = themes.wrap(pageChild);
       if (useSafeArea) {
         dialog = SafeArea(child: dialog);
diff --git a/packages/flutter/test/material/dialog_test.dart b/packages/flutter/test/material/dialog_test.dart
index 2e29042af5..fdf64ecb81 100644
--- a/packages/flutter/test/material/dialog_test.dart
+++ b/packages/flutter/test/material/dialog_test.dart
@@ -217,35 +217,7 @@ void main() {
     expect(materialWidget.shape, customBorder);
   });
 
-  testWidgets('showDialog child and builder cannot be simultaneously defined', (WidgetTester tester) async {
-    late BuildContext currentBuildContext;
-    await tester.pumpWidget(
-      MaterialApp(
-        home: Scaffold(
-          body: Center(
-            child: Builder(
-              builder: (BuildContext context) {
-                currentBuildContext = context;
-                return Container();
-              }
-            ),
-          ),
-        ),
-      ),
-    );
-
-    expect(() async {
-      showDialog<void>(
-        context: currentBuildContext,
-        child: const Text('Child'),
-        builder: (BuildContext context) {
-          return const Text('Builder');
-        },
-      );
-    }, throwsAssertionError);
-  });
-
-  testWidgets('showDialog child or builder must be defined', (WidgetTester tester) async {
+  testWidgets('showDialog builder must be defined', (WidgetTester tester) async {
     late BuildContext currentBuildContext;
     await tester.pumpWidget(
       MaterialApp(
diff --git a/packages/flutter/test_fixes/material.dart b/packages/flutter/test_fixes/material.dart
new file mode 100644
index 0000000000..eb7868cd23
--- /dev/null
+++ b/packages/flutter/test_fixes/material.dart
@@ -0,0 +1,10 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+void main() {
+  // Change made in https://github.com/flutter/flutter/pull/15303
+  showDialog(child: Text('Fix me.'));
+}
diff --git a/packages/flutter/test_fixes/material.dart.expect b/packages/flutter/test_fixes/material.dart.expect
new file mode 100644
index 0000000000..d21d0db8de
--- /dev/null
+++ b/packages/flutter/test_fixes/material.dart.expect
@@ -0,0 +1,10 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+void main() {
+  // Change made in https://github.com/flutter/flutter/pull/15303
+  showDialog(builder: (context) => Text('Fix me.'));
+}