diff --git a/packager/react-packager/src/node-haste/Module.js b/packager/react-packager/src/node-haste/Module.js
index 2a27dccfb..864846aef 100644
--- a/packager/react-packager/src/node-haste/Module.js
+++ b/packager/react-packager/src/node-haste/Module.js
@@ -18,14 +18,16 @@ const isAbsolutePath = require('absolute-path');
 const jsonStableStringify = require('json-stable-stringify');
 const path = require('path');
 
-type Extractor = (sourceCode: string) => {deps: {sync: Array<string>}};
+import type ModuleCache from './ModuleCache';
+
+export type Extractor = (sourceCode: string) => {deps: {sync: Array<string>}};
 type TransformedCode = {
   code?: string,
   dependencies?: Array<string>,
   dependencyOffsets?: Array<number>,
   map?: string,
 };
-type TransformCode = (
+export type TransformCode = (
   module: Module,
   sourceCode: string,
   transformOptions: mixed,
@@ -35,7 +37,7 @@ type TransformCode = (
   dependencyOffsets?: Array<number>,
   map?: string,
 }>;
-type Cache = {
+export type Cache = {
   get<T>(
     filePath: string,
     key: string,
@@ -43,15 +45,16 @@ type Cache = {
   ): Promise<T>,
   invalidate(filePath: string): void,
 };
-type Options = {cacheTransformResults?: boolean};
-type ModuleCache = {
-  getPackageForModule(m: Module): {
-    getName(): Promise<string>,
-    root: string,
-  },
+export type Options = {cacheTransformResults?: boolean};
+export type FastFs = {
+  readFile: (filePath: string) => Promise<string>,
+  closest: (innerFilePath: string, fileName: string) => string,
+  on: (
+    event: 'change',
+    onChange: (type: string, filePath: string, root: string) => void,
+  ) => FastFs,
 };
-type FastFs = {readFile: (filePath: string) => Promise<string>};
-type DepGraphHelpers = {isNodeModulesDir: (filePath: string) => boolean};
+export type DepGraphHelpers = {isNodeModulesDir: (filePath: string) => boolean};
 
 class Module {
 
diff --git a/packager/react-packager/src/node-haste/ModuleCache.js b/packager/react-packager/src/node-haste/ModuleCache.js
index 74a059a8e..4cdee4811 100644
--- a/packager/react-packager/src/node-haste/ModuleCache.js
+++ b/packager/react-packager/src/node-haste/ModuleCache.js
@@ -5,6 +5,8 @@
  * 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';
@@ -16,8 +18,29 @@ const Polyfill = require('./Polyfill');
 
 const path = require('path');
 
+import type {
+  Cache,
+  DepGraphHelpers,
+  FastFs,
+  Extractor,
+  TransformCode,
+  Options as ModuleOptions,
+} from './Module';
+
 class ModuleCache {
 
+  _moduleCache: {[filePath: string]: Module};
+  _packageCache: {[filePath: string]: Package};
+  _fastfs: FastFs;
+  _cache: Cache;
+  _extractRequires: Extractor;
+  _transformCode: TransformCode;
+  _depGraphHelpers: DepGraphHelpers;
+  _platforms: mixed;
+  _assetDependencies: mixed;
+  _moduleOptions: ModuleOptions;
+  _packageModuleMap: WeakMap<Module, string>;
+
   constructor({
     fastfs,
     cache,
@@ -26,7 +49,15 @@ class ModuleCache {
     depGraphHelpers,
     assetDependencies,
     moduleOptions,
-  }, platforms) {
+  }: {
+    fastfs: FastFs,
+    cache: Cache,
+    extractRequires: Extractor,
+    transformCode: TransformCode,
+    depGraphHelpers: DepGraphHelpers,
+    assetDependencies: mixed,
+    moduleOptions: ModuleOptions,
+  }, platforms: mixed) {
     this._moduleCache = Object.create(null);
     this._packageCache = Object.create(null);
     this._fastfs = fastfs;
@@ -42,7 +73,7 @@ class ModuleCache {
     fastfs.on('change', this._processFileChange.bind(this));
   }
 
-  getModule(filePath) {
+  getModule(filePath: string) {
     if (!this._moduleCache[filePath]) {
       this._moduleCache[filePath] = new Module({
         file: filePath,
@@ -62,7 +93,7 @@ class ModuleCache {
     return this._moduleCache;
   }
 
-  getAssetModule(filePath) {
+  getAssetModule(filePath: string) {
     if (!this._moduleCache[filePath]) {
       this._moduleCache[filePath] = new AssetModule({
         file: filePath,
@@ -75,7 +106,7 @@ class ModuleCache {
     return this._moduleCache[filePath];
   }
 
-  getPackage(filePath) {
+  getPackage(filePath: string) {
     if (!this._packageCache[filePath]) {
       this._packageCache[filePath] = new Package({
         file: filePath,
@@ -86,7 +117,7 @@ class ModuleCache {
     return this._packageCache[filePath];
   }
 
-  getPackageForModule(module) {
+  getPackageForModule(module: Module): ?Package {
     if (this._packageModuleMap.has(module)) {
       const packagePath = this._packageModuleMap.get(module);
       if (this._packageCache[packagePath]) {
@@ -105,7 +136,7 @@ class ModuleCache {
     return this.getPackage(packagePath);
   }
 
-  createPolyfill({file}) {
+  createPolyfill({file}: {file: string}) {
     return new Polyfill({
       file,
       cache: this._cache,