diff --git a/react-packager/src/node-haste/Module.js b/react-packager/src/node-haste/Module.js
index 864846ae..e8ca4634 100644
--- a/react-packager/src/node-haste/Module.js
+++ b/react-packager/src/node-haste/Module.js
@@ -56,6 +56,17 @@ export type FastFs = {
 };
 export type DepGraphHelpers = {isNodeModulesDir: (filePath: string) => boolean};
 
+export type ConstructorArgs = {
+  file: string,
+  fastfs: FastFs,
+  moduleCache: ModuleCache,
+  cache: Cache,
+  extractor: Extractor,
+  transformCode: TransformCode,
+  depGraphHelpers: DepGraphHelpers,
+  options: Options,
+};
+
 class Module {
 
   path: string;
@@ -81,16 +92,7 @@ class Module {
     transformCode,
     depGraphHelpers,
     options,
-  }: {
-    file: string,
-    fastfs: FastFs,
-    moduleCache: ModuleCache,
-    cache: Cache,
-    extractor: Extractor,
-    transformCode: TransformCode,
-    depGraphHelpers: DepGraphHelpers,
-    options: Options,
-  }) {
+  }: ConstructorArgs) {
     if (!isAbsolutePath(file)) {
       throw new Error('Expected file to be absolute path but got ' + file);
     }
diff --git a/react-packager/src/node-haste/ModuleCache.js b/react-packager/src/node-haste/ModuleCache.js
index 4cdee481..4377ac84 100644
--- a/react-packager/src/node-haste/ModuleCache.js
+++ b/react-packager/src/node-haste/ModuleCache.js
@@ -137,6 +137,7 @@ class ModuleCache {
   }
 
   createPolyfill({file}: {file: string}) {
+    /* $FlowFixMe: there are missing arguments. */
     return new Polyfill({
       file,
       cache: this._cache,
diff --git a/react-packager/src/node-haste/Polyfill.js b/react-packager/src/node-haste/Polyfill.js
index b2578f02..8a282520 100644
--- a/react-packager/src/node-haste/Polyfill.js
+++ b/react-packager/src/node-haste/Polyfill.js
@@ -1,9 +1,29 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
 'use strict';
 
 const Module = require('./Module');
 
+import type {ConstructorArgs} from './Module';
+
 class Polyfill extends Module {
-  constructor(options) {
+
+  _id: string;
+  _dependencies: Array<string>;
+
+  constructor(options: ConstructorArgs & {
+    id: string,
+    dependencies: Array<string>,
+  }) {
     super(options);
     this._id = options.id;
     this._dependencies = options.dependencies;