diff --git a/web_sdk/BUILD.gn b/web_sdk/BUILD.gn
index 78d8b290825..f7d9267a237 100644
--- a/web_sdk/BUILD.gn
+++ b/web_sdk/BUILD.gn
@@ -45,14 +45,16 @@ prebuilt_dart_action("web_ui_sources") {
   output_dir = rebase_path("$root_out_dir/flutter_web_sdk/lib/ui/")
   input_dir = rebase_path("//flutter/lib/web_ui/lib/")
 
+  outputs = [
+    "$target_gen_dir/$target_name.stamp",
+  ]
+
   args = [
     "--output-dir=$output_dir",
     "--input-dir=$input_dir",
     "--ui",
-  ]
-
-  outputs = [
-    "$root_out_dir/flutter_web_engine_sdk_stamp",
+    "--stamp",
+    rebase_path(outputs[0], root_build_dir),
   ]
 
   foreach(source_file, web_ui_sources) {
@@ -69,14 +71,16 @@ prebuilt_dart_action("web_engine_sources") {
   output_dir = rebase_path("$root_out_dir/flutter_web_sdk/lib/_engine/")
   input_dir = rebase_path("//flutter/lib/web_ui/lib/src/")
 
+  outputs = [
+    "$target_gen_dir/$target_name.stamp",
+  ]
+
   args = [
     "--output-dir=$output_dir",
     "--input-dir=$input_dir",
     "--engine",
-  ]
-
-  outputs = [
-    "$root_out_dir/flutter_web_sdk_stamp",
+    "--stamp",
+    rebase_path(outputs[0], root_build_dir),
   ]
 
   foreach(source_file, web_engine_sources) {
diff --git a/web_sdk/sdk_rewriter.dart b/web_sdk/sdk_rewriter.dart
index ad49a3d4afa..dad61012a05 100644
--- a/web_sdk/sdk_rewriter.dart
+++ b/web_sdk/sdk_rewriter.dart
@@ -12,24 +12,25 @@ final ArgParser argParser = ArgParser()
   ..addOption('input-dir')
   ..addFlag('ui', defaultsTo: false)
   ..addFlag('engine', defaultsTo: false)
-  ..addMultiOption('input');
+  ..addMultiOption('input')
+  ..addOption('stamp');
 
 const List<List<String>> uiPatterns = <List<String>>[
   <String>['library ui;', 'library dart.ui;'],
   <String>['part of ui;', 'part of dart.ui;'],
   <String>[
-r'''
+    r'''
 import 'src/engine.dart' as engine;
 ''',
-r'''
+    r'''
 import 'dart:_engine' as engine;
 '''
   ],
   <String>[
-r'''
+    r'''
 export 'src/engine.dart'
 ''',
-r'''
+    r'''
 export 'dart:_engine'
 ''',
   ]
@@ -39,17 +40,17 @@ const List<List<String>> enginePatterns = <List<String>>[
   <String>['library engine;', 'library dart._engine;'],
   <String>['part of engine;', 'part of dart._engine;'],
   <String>[
-r'''
+    r'''
 import '../ui.dart' as ui;
 ''',
-r'''
+    r'''
 import 'dart:ui' as ui;
 '''
   ]
 ];
 
 const List<List<String>> sharedPatterns = <List<String>>[
-  <String>["import 'package:meta/meta.dart';" ,''],
+  <String>["import 'package:meta/meta.dart';", ''],
   <String>['@required', ''],
   <String>['@protected', ''],
   <String>['@mustCallSuper', ''],
@@ -65,7 +66,8 @@ void main(List<String> arguments) {
   final String inputDirectoryPath = results['input-dir'];
   for (String inputFilePath in results['input']) {
     final File inputFile = File(inputFilePath);
-    final File outputFile = File(path.join(directory.path, inputFile.path.substring(inputDirectoryPath.length)))
+    final File outputFile = File(path.join(
+        directory.path, inputFile.path.substring(inputDirectoryPath.length)))
       ..createSync(recursive: true);
     String source = inputFile.readAsStringSync();
     final List<List<String>> replacementPatterns = <List<String>>[];
@@ -79,5 +81,8 @@ void main(List<String> arguments) {
       source = source.replaceAll(patterns.first, patterns.last);
     }
     outputFile.writeAsStringSync(source);
+    if (results['stamp'] != null) {
+      File(results['stamp']).writeAsStringSync("stamp");
+    }
   }
 }