diff --git a/packager/src/ModuleGraph/node-haste/node-haste.js b/packager/src/ModuleGraph/node-haste/node-haste.js
index c3a136727..966e248d2 100644
--- a/packager/src/ModuleGraph/node-haste/node-haste.js
+++ b/packager/src/ModuleGraph/node-haste/node-haste.js
@@ -46,12 +46,12 @@ const platforms = new Set(defaults.platforms);
  */
 function getFakeModuleMap(hasteMap: HasteMap) {
   return {
-    getModule(name: string, platform_: string): ?string {
-      const module = hasteMap.getModule(name, platform_);
+    getModule(name: string, platform: ?string): ?string {
+      const module = hasteMap.getModule(name, platform);
       return module && module.type === 'Module' ? module.path : null;
     },
-    getPackage(name: string, platform_: string): ?string {
-      const module = hasteMap.getModule(name, platform_);
+    getPackage(name: string, platform: ?string): ?string {
+      const module = hasteMap.getModule(name, platform);
       return module && module.type === 'Package' ? module.path : null;
     },
   };
diff --git a/packager/src/node-haste/DependencyGraph/ResolutionRequest.js b/packager/src/node-haste/DependencyGraph/ResolutionRequest.js
index eca28e640..a937ed74c 100644
--- a/packager/src/node-haste/DependencyGraph/ResolutionRequest.js
+++ b/packager/src/node-haste/DependencyGraph/ResolutionRequest.js
@@ -33,8 +33,8 @@ type DirExistsFn = (filePath: string) => boolean;
  * `jest-haste-map`'s interface for ModuleMap.
  */
 export type ModuleMap = {
-  getModule(name: string, platform: string, supportsNativePlatform: boolean): ?string,
-  getPackage(name: string, platform: string, supportsNativePlatform: boolean): ?string,
+  getModule(name: string, platform: ?string, supportsNativePlatform: boolean): ?string,
+  getPackage(name: string, platform: ?string, supportsNativePlatform: boolean): ?string,
 };
 
 type Packageish = {
@@ -68,7 +68,7 @@ type Options<TModule, TPackage> = {|
   +matchFiles: MatchFilesByDirAndPattern,
   +moduleCache: ModuleishCache<TModule, TPackage>,
   +moduleMap: ModuleMap,
-  +platform: string,
+  +platform: ?string,
   +platforms: Set<string>,
   +preferNativePlatform: boolean,
 |};
@@ -99,7 +99,7 @@ class ResolutionRequest<TModule: Moduleish, TPackage: Packageish> {
   _matchFiles: MatchFilesByDirAndPattern;
   _moduleCache: ModuleishCache<TModule, TPackage>;
   _moduleMap: ModuleMap;
-  _platform: string;
+  _platform: ?string;
   _platforms: Set<string>;
   _preferNativePlatform: boolean;
   static emptyModule: string;
diff --git a/packager/src/node-haste/index.js b/packager/src/node-haste/index.js
index 4f6311141..ad4a843ba 100644
--- a/packager/src/node-haste/index.js
+++ b/packager/src/node-haste/index.js
@@ -209,7 +209,7 @@ class DependencyGraph extends EventEmitter {
     recursive = true,
   }: {
     entryPath: string,
-    platform: string,
+    platform: ?string,
     transformOptions: TransformOptions,
     onProgress?: ?(finishedModules: number, totalModules: number) => mixed,
     recursive: boolean,
@@ -254,7 +254,7 @@ class DependencyGraph extends EventEmitter {
     return Promise.resolve(this._hasteFS.matchFiles(pattern));
   }
 
-  _getRequestPlatform(entryPath: string, platform: string) {
+  _getRequestPlatform(entryPath: string, platform: ?string): ?string {
     if (platform == null) {
       platform = getPlatformExtension(entryPath, this._opts.platforms);
     } else if (!this._opts.platforms.has(platform)) {
diff --git a/packager/src/node-haste/lib/getAssetDataFromName.js b/packager/src/node-haste/lib/getAssetDataFromName.js
index 86be496c9..e41279188 100644
--- a/packager/src/node-haste/lib/getAssetDataFromName.js
+++ b/packager/src/node-haste/lib/getAssetDataFromName.js
@@ -5,13 +5,22 @@
  * 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 getPlatformExtension = require('./getPlatformExtension');
 const path = require('path');
 
-function getAssetDataFromName(filename, platforms) {
+function getAssetDataFromName(filename: string, platforms: Set<string>): {|
+  assetName: string,
+  name: string,
+  platform: ?string,
+  resolution: number,
+  type: string,
+|} {
   const ext = path.extname(filename);
   const platformExt = getPlatformExtension(filename, platforms);
 
@@ -45,11 +54,11 @@ function getAssetDataFromName(filename, platforms) {
   assetName = decodeURIComponent(assetName);
 
   return {
-    resolution,
     assetName,
-    type: ext.slice(1),
     name: path.basename(assetName, ext),
     platform: platformExt,
+    resolution,
+    type: ext.slice(1),
   };
 }
 
diff --git a/packager/src/node-haste/lib/getPlatformExtension.js b/packager/src/node-haste/lib/getPlatformExtension.js
index 6f5058333..bc3bf7f81 100644
--- a/packager/src/node-haste/lib/getPlatformExtension.js
+++ b/packager/src/node-haste/lib/getPlatformExtension.js
@@ -5,7 +5,10 @@
  * 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 SUPPORTED_PLATFORM_EXTS = new Set([
@@ -15,7 +18,10 @@ const SUPPORTED_PLATFORM_EXTS = new Set([
 ]);
 
 // Extract platform extension: index.ios.js -> ios
-function getPlatformExtension(file, platforms = SUPPORTED_PLATFORM_EXTS) {
+function getPlatformExtension(
+  file: string,
+  platforms: Set<string> = SUPPORTED_PLATFORM_EXTS,
+): ?string {
   const last = file.lastIndexOf('.');
   const secondToLast = file.lastIndexOf('.', last - 1);
   if (secondToLast === -1) {