diff --git a/packager/react-packager/src/JSTransformer/index.js b/packager/react-packager/src/JSTransformer/index.js
index ad4b7df21..b2337dd71 100644
--- a/packager/react-packager/src/JSTransformer/index.js
+++ b/packager/react-packager/src/JSTransformer/index.js
@@ -21,6 +21,7 @@ const workerFarm = require('worker-farm');
 const debug = require('debug')('ReactNativePackager:JStransformer');
 
 import type {Data as TransformData, Options as TransformOptions} from './worker/worker';
+import type {SourceMap} from '../lib/SourceMap';
 
 // Avoid memory leaks caused in workers. This number seems to be a good enough number
 // to avoid any memory leak while not slowing down initial builds.
@@ -109,8 +110,8 @@ class Transformer {
   minify: (
     filename: string,
     code: string,
-    sourceMap: string,
-  ) => Promise<mixed>;
+    sourceMap: SourceMap,
+  ) => Promise<{code: string, map: SourceMap}>;
 
   constructor(options: Options) {
     const opts = this._opts = validateOpts(options);
diff --git a/packager/react-packager/src/Resolver/index.js b/packager/react-packager/src/Resolver/index.js
index 0283498da..31e99496d 100644
--- a/packager/react-packager/src/Resolver/index.js
+++ b/packager/react-packager/src/Resolver/index.js
@@ -22,60 +22,27 @@ import type Module from '../node-haste/Module';
 import type {SourceMap} from '../lib/SourceMap';
 import type {Options as TransformOptions} from '../JSTransformer/worker/worker';
 import type {Reporter} from '../lib/reporting';
+import type {TransformCode} from '../node-haste/Module';
+import type Cache from '../node-haste/Cache';
 
-const validateOpts = declareOpts({
-  projectRoots: {
-    type: 'array',
-    required: true,
-  },
-  blacklistRE: {
-    type: 'object', // typeof regex is object
-  },
-  polyfillModuleNames: {
-    type: 'array',
-    default: [],
-  },
-  moduleFormat: {
-    type: 'string',
-    default: 'haste',
-  },
-  watch: {
-    type: 'boolean',
-    default: false,
-  },
-  assetExts: {
-    type: 'array',
-    required: true,
-  },
-  platforms: {
-    type: 'array',
-    required: true,
-  },
-  cache: {
-    type: 'object',
-    required: true,
-  },
-  transformCode: {
-    type: 'function',
-  },
-  transformCacheKey: {
-    type: 'string',
-  },
-  extraNodeModules: {
-    type: 'object',
-    required: false,
-  },
-  minifyCode: {
-    type: 'function',
-  },
-  resetCache: {
-    type: 'boolean',
-    default: false,
-  },
-  reporter: {
-    type: 'object',
-  },
-});
+type MinifyCode = (filePath: string, code: string, map: SourceMap) =>
+  Promise<{code: string, map: SourceMap}>;
+
+type Options = {
+  assetExts: Array<string>,
+  blacklistRE?: RegExp,
+  cache: Cache,
+  extraNodeModules?: {},
+  minifyCode: MinifyCode,
+  platforms: Array<string>,
+  polyfillModuleNames?: Array<string>,
+  projectRoots: Array<string>,
+  reporter: Reporter,
+  resetCache: boolean,
+  transformCacheKey: string,
+  transformCode: TransformCode,
+  watch?: boolean,
+};
 
 const getDependenciesValidateOpts = declareOpts({
   dev: {
@@ -99,16 +66,10 @@ const getDependenciesValidateOpts = declareOpts({
 class Resolver {
 
   _depGraph: DependencyGraph;
-  _minifyCode: (filePath: string, code: string, map: SourceMap) =>
-    Promise<{code: string, map: SourceMap}>;
+  _minifyCode: MinifyCode;
   _polyfillModuleNames: Array<string>;
 
-  constructor(options: {
-    reporter: Reporter,
-    resetCache: boolean,
-  }) {
-    const opts = validateOpts(options);
-
+  constructor(opts: Options) {
     this._depGraph = new DependencyGraph({
       assetDependencies: ['react-native/Libraries/Image/AssetRegistry'],
       assetExts: opts.assetExts,
@@ -116,21 +77,21 @@ class Resolver {
       extraNodeModules: opts.extraNodeModules,
       ignoreFilePath: function(filepath) {
         return filepath.indexOf('__tests__') !== -1 ||
-          (opts.blacklistRE && opts.blacklistRE.test(filepath));
+          (opts.blacklistRE != null && opts.blacklistRE.test(filepath));
       },
       moduleOptions: {
         cacheTransformResults: true,
-        resetCache: options.resetCache,
+        resetCache: opts.resetCache,
       },
       platforms: opts.platforms,
       preferNativePlatform: true,
       providesModuleNodeModules: defaults.providesModuleNodeModules,
-      reporter: options.reporter,
-      resetCache: options.resetCache,
+      reporter: opts.reporter,
+      resetCache: opts.resetCache,
       roots: opts.projectRoots,
       transformCacheKey: opts.transformCacheKey,
       transformCode: opts.transformCode,
-      watch: opts.watch,
+      watch: opts.watch || false,
     });
 
     this._minifyCode = opts.minifyCode;
diff --git a/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js b/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js
index ec4b67df7..7c9a7721d 100644
--- a/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js
+++ b/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js
@@ -32,7 +32,7 @@ type DirExistsFn = (filePath: string) => boolean;
 type Options = {
   dirExists: DirExistsFn,
   entryPath: string,
-  extraNodeModules: Object,
+  extraNodeModules: ?Object,
   hasteFS: HasteFS,
   hasteMap: HasteMap,
   helpers: DependencyGraphHelpers,
@@ -46,7 +46,7 @@ type Options = {
 class ResolutionRequest {
   _dirExists: DirExistsFn;
   _entryPath: string;
-  _extraNodeModules: Object;
+  _extraNodeModules: ?Object;
   _hasteFS: HasteFS;
   _hasteMap: HasteMap;
   _helpers: DependencyGraphHelpers;
@@ -338,10 +338,11 @@ class ResolutionRequest {
           }
 
           if (this._extraNodeModules) {
+            const {_extraNodeModules} = this;
             const bits = toModuleName.split('/');
             const packageName = bits[0];
-            if (this._extraNodeModules[packageName]) {
-              bits[0] = this._extraNodeModules[packageName];
+            if (_extraNodeModules[packageName]) {
+              bits[0] = _extraNodeModules[packageName];
               searchQueue.push(path.join.apply(path, bits));
             }
           }
diff --git a/packager/react-packager/src/node-haste/index.js b/packager/react-packager/src/node-haste/index.js
index be128dee3..13ded6d58 100644
--- a/packager/react-packager/src/node-haste/index.js
+++ b/packager/react-packager/src/node-haste/index.js
@@ -51,7 +51,7 @@ class DependencyGraph {
   _opts: {|
     assetExts: Array<string>,
     extensions: Array<string>,
-    extraNodeModules: Object,
+    extraNodeModules: ?Object,
     forceNodeFilesystemAPI: boolean,
     ignoreFilePath: (filePath: string) => boolean,
     maxWorkers: ?number,
@@ -107,7 +107,7 @@ class DependencyGraph {
     assetExts: Array<string>,
     cache: Cache,
     extensions?: ?Array<string>,
-    extraNodeModules: Object,
+    extraNodeModules: ?Object,
     forceNodeFilesystemAPI?: boolean,
     ignoreFilePath: (filePath: string) => boolean,
     maxWorkers?: ?number,