diff --git a/packages/metro-bundler/src/Bundler/index.js b/packages/metro-bundler/src/Bundler/index.js
index e2d8fc8f..c5119278 100644
--- a/packages/metro-bundler/src/Bundler/index.js
+++ b/packages/metro-bundler/src/Bundler/index.js
@@ -89,27 +89,26 @@ const assetPropertyBlacklist = new Set([
   'path',
 ]);
 
-type Options = {
-  allowBundleUpdates: boolean,
-  assetExts: Array<string>,
-  assetServer: AssetServer,
-  blacklistRE?: RegExp,
-  cacheVersion: string,
-  extraNodeModules: {},
-  getTransformOptions?: GetTransformOptions,
-  globalTransformCache: ?GlobalTransformCache,
-  hasteImpl?: HasteImpl,
-  moduleFormat: string,
-  platforms: Array<string>,
-  polyfillModuleNames: Array<string>,
-  projectRoots: Array<string>,
-  providesModuleNodeModules?: Array<string>,
-  reporter: Reporter,
-  resetCache: boolean,
-  transformModulePath?: string,
-  transformTimeoutInterval: ?number,
-  watch: boolean,
-};
+type Options = {|
+  +allowBundleUpdates: boolean,
+  +assetExts: Array<string>,
+  +assetServer: AssetServer,
+  +blacklistRE?: RegExp,
+  +cacheVersion: string,
+  +extraNodeModules: {},
+  +getTransformOptions?: GetTransformOptions,
+  +globalTransformCache: ?GlobalTransformCache,
+  +hasteImpl?: HasteImpl,
+  +platforms: Array<string>,
+  +polyfillModuleNames: Array<string>,
+  +projectRoots: Array<string>,
+  +providesModuleNodeModules?: Array<string>,
+  +reporter: Reporter,
+  +resetCache: boolean,
+  +transformModulePath?: string,
+  +transformTimeoutInterval: ?number,
+  +watch: boolean,
+|};
 
 class Bundler {
 
@@ -190,7 +189,6 @@ class Bundler {
       hasteImpl: opts.hasteImpl,
       maxWorkerCount,
       minifyCode: this._transformer.minify,
-      moduleFormat: opts.moduleFormat,
       platforms: new Set(opts.platforms),
       polyfillModuleNames: opts.polyfillModuleNames,
       projectRoots: opts.projectRoots,
diff --git a/packages/metro-bundler/src/Resolver/index.js b/packages/metro-bundler/src/Resolver/index.js
index 3538524b..58b14622 100644
--- a/packages/metro-bundler/src/Resolver/index.js
+++ b/packages/metro-bundler/src/Resolver/index.js
@@ -29,25 +29,25 @@ import type {GlobalTransformCache} from '../lib/GlobalTransformCache';
 type MinifyCode = (filePath: string, code: string, map: SourceMap) =>
   Promise<{code: string, map: SourceMap}>;
 
-type Options = {
-  assetExts: Array<string>,
-  blacklistRE?: RegExp,
-  cache: Cache,
-  extraNodeModules: ?{},
-  getTransformCacheKey: GetTransformCacheKey,
-  globalTransformCache: ?GlobalTransformCache,
-  hasteImpl?: HasteImpl,
-  maxWorkerCount: number,
-  minifyCode: MinifyCode,
-  platforms: Set<string>,
-  polyfillModuleNames?: Array<string>,
-  projectRoots: Array<string>,
-  providesModuleNodeModules: Array<string>,
-  reporter: Reporter,
-  resetCache: boolean,
-  transformCode: TransformCode,
-  watch: boolean,
-};
+type Options = {|
+  +assetExts: Array<string>,
+  +blacklistRE?: RegExp,
+  +cache: Cache,
+  +extraNodeModules: ?{},
+  +getTransformCacheKey: GetTransformCacheKey,
+  +globalTransformCache: ?GlobalTransformCache,
+  +hasteImpl?: HasteImpl,
+  +maxWorkerCount: number,
+  +minifyCode: MinifyCode,
+  +platforms: Set<string>,
+  +polyfillModuleNames?: Array<string>,
+  +projectRoots: Array<string>,
+  +providesModuleNodeModules: Array<string>,
+  +reporter: Reporter,
+  +resetCache: boolean,
+  +transformCode: TransformCode,
+  +watch: boolean,
+|};
 
 class Resolver {
 
@@ -70,7 +70,6 @@ class Resolver {
         return filepath.indexOf('__tests__') !== -1 ||
           (opts.blacklistRE != null && opts.blacklistRE.test(filepath));
       },
-      maxWorkers: null,
       moduleOptions: {
         cacheTransformResults: true,
         hasteImpl: opts.hasteImpl,
diff --git a/packages/metro-bundler/src/node-haste/DependencyGraph/DependencyGraphHelpers.js b/packages/metro-bundler/src/node-haste/DependencyGraph/DependencyGraphHelpers.js
index bebfaf62..83af2327 100644
--- a/packages/metro-bundler/src/node-haste/DependencyGraph/DependencyGraphHelpers.js
+++ b/packages/metro-bundler/src/node-haste/DependencyGraph/DependencyGraphHelpers.js
@@ -21,8 +21,8 @@ class DependencyGraphHelpers {
   _assetExts: Array<string>;
 
   constructor({providesModuleNodeModules, assetExts}: {
-    providesModuleNodeModules: Array<string>,
-    assetExts: Array<string>,
+    +providesModuleNodeModules: Array<string>,
+    +assetExts: Array<string>,
   }) {
     this._providesModuleNodeModules = providesModuleNodeModules;
     this._assetExts = assetExts;
diff --git a/packages/metro-bundler/src/node-haste/index.js b/packages/metro-bundler/src/node-haste/index.js
index 66ce8452..cbb67c94 100644
--- a/packages/metro-bundler/src/node-haste/index.js
+++ b/packages/metro-bundler/src/node-haste/index.js
@@ -49,28 +49,28 @@ import type {
 } from './Module';
 import type {HasteFS} from './types';
 
-type Options = {
-  assetDependencies: Array<string>,
-  assetExts: Array<string>,
-  cache: Cache,
-  extensions: Array<string>,
-  extraNodeModules: ?{},
-  forceNodeFilesystemAPI: boolean,
-  getTransformCacheKey: GetTransformCacheKey,
-  globalTransformCache: ?GlobalTransformCache,
-  ignoreFilePath: (filePath: string) => boolean,
-  maxWorkerCount: number,
-  moduleOptions: ModuleOptions,
-  platforms: Set<string>,
-  preferNativePlatform: boolean,
-  providesModuleNodeModules: Array<string>,
-  reporter: Reporter,
-  resetCache: boolean,
-  roots: Array<string>,
-  transformCode: TransformCode,
-  useWatchman: boolean,
-  watch: boolean,
-};
+type Options = {|
+  +assetDependencies: Array<string>,
+  +assetExts: Array<string>,
+  +cache: Cache,
+  +extensions: Array<string>,
+  +extraNodeModules: ?{},
+  +forceNodeFilesystemAPI: boolean,
+  +getTransformCacheKey: GetTransformCacheKey,
+  +globalTransformCache: ?GlobalTransformCache,
+  +ignoreFilePath: (filePath: string) => boolean,
+  +maxWorkerCount: number,
+  +moduleOptions: ModuleOptions,
+  +platforms: Set<string>,
+  +preferNativePlatform: boolean,
+  +providesModuleNodeModules: Array<string>,
+  +reporter: Reporter,
+  +resetCache: boolean,
+  +roots: Array<string>,
+  +transformCode: TransformCode,
+  +useWatchman: boolean,
+  +watch: boolean,
+|};
 
 const JEST_HASTE_MAP_CACHE_BREAKER = 1;
 
@@ -84,12 +84,12 @@ class DependencyGraph extends EventEmitter {
   _hasteFS: HasteFS;
   _moduleMap: ModuleMap;
 
-  constructor(config: {
-    opts: Options,
-    haste: JestHasteMap,
-    initialHasteFS: HasteFS,
-    initialModuleMap: ModuleMap,
-  }) {
+  constructor(config: {|
+    +opts: Options,
+    +haste: JestHasteMap,
+    +initialHasteFS: HasteFS,
+    +initialModuleMap: ModuleMap,
+  |}) {
     super();
     invariant(config.opts.maxWorkerCount >= 1, 'worker count must be greater or equal to 1');
     this._opts = config.opts;