diff --git a/local-cli/bundle/buildBundle.js b/local-cli/bundle/buildBundle.js
index 3aa739ab3..97be14d79 100644
--- a/local-cli/bundle/buildBundle.js
+++ b/local-cli/bundle/buildBundle.js
@@ -19,6 +19,7 @@ const outputBundle = require('./output/bundle');
 const path = require('path');
 const saveAssets = require('./saveAssets');
 const defaultAssetExts = require('../../packager/defaults').assetExts;
+const defaultSourceExts = require('../../packager/defaults').sourceExts;
 const defaultPlatforms = require('../../packager/defaults').platforms;
 const defaultProvidesModuleNodeModules = require('../../packager/defaults').providesModuleNodeModules;
 
@@ -64,6 +65,7 @@ function buildBundle(
   var shouldClosePackager = false;
   if (!packagerInstance) {
     const assetExts = (config.getAssetExts && config.getAssetExts()) || [];
+    const sourceExts = (config.getSourceExts && config.getSourceExts()) || [];
     const platforms = (config.getPlatforms && config.getPlatforms()) || [];
 
     const transformModulePath =
@@ -88,6 +90,7 @@ function buildBundle(
       providesModuleNodeModules: providesModuleNodeModules,
       resetCache: args.resetCache,
       reporter: new TerminalReporter(),
+      sourceExts: defaultSourceExts.concat(sourceExts),
       transformModulePath: transformModulePath,
       watch: false,
     };
diff --git a/local-cli/server/runServer.js b/local-cli/server/runServer.js
index 870bf0b99..ca3146210 100644
--- a/local-cli/server/runServer.js
+++ b/local-cli/server/runServer.js
@@ -16,6 +16,7 @@ const connect = require('connect');
 const copyToClipBoardMiddleware = require('./middleware/copyToClipBoardMiddleware');
 const cpuProfilerMiddleware = require('./middleware/cpuProfilerMiddleware');
 const defaultAssetExts = require('../../packager/defaults').assetExts;
+const defaultSourceExts = require('../../packager/defaults').sourceExts;
 const defaultPlatforms = require('../../packager/defaults').platforms;
 const defaultProvidesModuleNodeModules = require('../../packager/defaults').providesModuleNodeModules;
 const getDevToolsMiddleware = require('./middleware/getDevToolsMiddleware');
@@ -93,7 +94,7 @@ function getPackagerServer(args, config) {
       // First we let require resolve it, so we can require packages in node_modules
       // as expected. eg: require('my-package/reporter');
       LogReporter = require(args.customLogReporterPath);
-    } catch(e) {
+    } catch (e) {
       // If that doesn't work, then we next try relative to the cwd, eg:
       // require('./reporter');
       LogReporter = require(path.resolve(args.customLogReporterPath));
@@ -116,6 +117,7 @@ function getPackagerServer(args, config) {
     providesModuleNodeModules: providesModuleNodeModules,
     reporter: new LogReporter(),
     resetCache: args.resetCache,
+    sourceExts: defaultSourceExts.concat(args.sourceExts),
     transformModulePath: transformModulePath,
     verbose: args.verbose,
     watch: !args.nonPersistent,
diff --git a/local-cli/server/server.js b/local-cli/server/server.js
index 4825fc9a0..110db66ee 100644
--- a/local-cli/server/server.js
+++ b/local-cli/server/server.js
@@ -67,9 +67,14 @@ module.exports = {
     default: (config) => config.getProjectRoots(),
   }, {
     command: '--assetExts [list]',
-    description: 'Specify any additional asset extentions to be used by the packager',
+    description: 'Specify any additional asset extensions to be used by the packager',
     parse: (val) => val.split(','),
     default: (config) => config.getAssetExts(),
+  }, {
+    command: '--sourceExts [list]',
+    description: 'Specify any additional source extensions to be used by the packager',
+    parse: (val) => val.split(','),
+    default: (config) => config.getSourceExts(),
   }, {
     command: '--platforms [list]',
     description: 'Specify any additional platforms to be used by the packager',
diff --git a/local-cli/util/Config.js b/local-cli/util/Config.js
index 68b91eb60..987046bae 100644
--- a/local-cli/util/Config.js
+++ b/local-cli/util/Config.js
@@ -28,7 +28,7 @@ import type {HasteImpl} from '../../packager/src/node-haste/Module';
 export type ConfigT = {
   extraNodeModules: {[id: string]: string},
   /**
-   * Specify any additional asset extentions to be used by the packager.
+   * Specify any additional asset file extensions to be used by the packager.
    * For example, if you want to include a .ttf file, you would return ['ttf']
    * from here and use `require('./fonts/example.ttf')` inside your app.
    */
@@ -54,6 +54,15 @@ export type ConfigT = {
    * providesModule declarations.
    */
   getProvidesModuleNodeModules?: () => Array<string>,
+
+  /**
+   * Specify any additional source file extensions to be used by the packager.
+   * For example, if you want to include a .ts file, you would return ['ts']
+   * from here and use `require('./module/example')` to require the file with
+   * path 'module/example.ts' inside your app.
+   */
+  getSourceExts: () => Array<string>,
+
   /**
    * Returns the path to a custom transformer. This can also be overridden
    * with the --transformer commandline argument.
@@ -90,6 +99,7 @@ const defaultConfig: ConfigT = {
   getPlatforms: () => [],
   getProjectRoots: () => [process.cwd()],
   getProvidesModuleNodeModules: () => providesModuleNodeModules.slice(),
+  getSourceExts: () => [],
   getTransformModulePath: () => path.resolve(__dirname, '../../packager/transformer'),
   getTransformOptions: async () => ({}),
   postMinifyProcess: x => x,
diff --git a/packager/defaults.js b/packager/defaults.js
index 119396977..7f6c2e721 100644
--- a/packager/defaults.js
+++ b/packager/defaults.js
@@ -10,13 +10,15 @@
  */
 'use strict';
 
-exports.assetExts =  [
+exports.assetExts = [
   'bmp', 'gif', 'jpg', 'jpeg', 'png', 'psd', 'svg', 'webp', // Image formats
   'm4v', 'mov', 'mp4', 'mpeg', 'mpg', 'webm', // Video formats
   'aac', 'aiff', 'caf', 'm4a', 'mp3', 'wav', // Audio formats
   'html', 'pdf', // Document formats
 ];
 
+exports.sourceExts = ['js', 'json'];
+
 exports.moduleSystem = require.resolve('./src/Resolver/polyfills/require.js');
 
 exports.platforms = ['ios', 'android', 'windows', 'web'];
diff --git a/packager/react-packager.js b/packager/react-packager.js
index 079b42ac8..24d001c1d 100644
--- a/packager/react-packager.js
+++ b/packager/react-packager.js
@@ -16,8 +16,8 @@ const Logger = require('./src/Logger');
 const debug = require('debug');
 const invariant = require('fbjs/lib/invariant');
 
-import type Server from './src/Server';
 import type {PostProcessModules, PostMinifyProcess} from './src/Bundler';
+import type Server from './src/Server';
 import type {GlobalTransformCache} from './src/lib/GlobalTransformCache';
 import type {Reporter} from './src/lib/reporting';
 import type {HasteImpl} from './src/node-haste/Module';
@@ -33,6 +33,7 @@ type Options = {
   postMinifyProcess?: PostMinifyProcess,
   projectRoots: Array<string>,
   reporter?: Reporter,
+  +sourceExts: ?Array<string>,
   watch?: boolean,
 };
 
diff --git a/packager/rn-cli.config.js b/packager/rn-cli.config.js
index 3f6f4fd54..3b398c7d1 100644
--- a/packager/rn-cli.config.js
+++ b/packager/rn-cli.config.js
@@ -22,6 +22,10 @@ module.exports = {
     return [];
   },
 
+  getSourceExts() {
+    return [];
+  },
+
   getBlacklistRE() {
     return blacklist();
   },
diff --git a/packager/src/Bundler/__tests__/Bundler-test.js b/packager/src/Bundler/__tests__/Bundler-test.js
index 9100b766c..dcea0d6e1 100644
--- a/packager/src/Bundler/__tests__/Bundler-test.js
+++ b/packager/src/Bundler/__tests__/Bundler-test.js
@@ -44,6 +44,7 @@ var commonOptions = {
   extraNodeModules: {},
   platforms: defaults.platforms,
   resetCache: false,
+  sourceExts: defaults.sourceExts,
   watch: false,
 };
 
diff --git a/packager/src/Bundler/index.js b/packager/src/Bundler/index.js
index 03396550c..628ffcbc0 100644
--- a/packager/src/Bundler/index.js
+++ b/packager/src/Bundler/index.js
@@ -132,6 +132,7 @@ type Options = {|
   +providesModuleNodeModules?: Array<string>,
   +reporter: Reporter,
   +resetCache: boolean,
+  +sourceExts: Array<string>,
   +transformModulePath?: string,
   +transformTimeoutInterval: ?number,
   +watch: boolean,
@@ -217,6 +218,7 @@ class Bundler {
         opts.providesModuleNodeModules || defaults.providesModuleNodeModules,
       reporter: opts.reporter,
       resetCache: opts.resetCache,
+      sourceExts: opts.sourceExts,
       transformCode:
         (module, code, transformCodeOptions) => this._transformer.transformFile(
           module.path,
diff --git a/packager/src/ModuleGraph/node-haste/node-haste.js b/packager/src/ModuleGraph/node-haste/node-haste.js
index fd3e48df3..ac93bde1c 100644
--- a/packager/src/ModuleGraph/node-haste/node-haste.js
+++ b/packager/src/ModuleGraph/node-haste/node-haste.js
@@ -34,6 +34,7 @@ const defaults = require('../../../defaults');
 type ResolveOptions = {|
   assetExts: Extensions,
   extraNodeModules: {[id: string]: string},
+  +sourceExts: Extensions,
   transformedFiles: {[path: Path]: TransformedCodeFile},
 |};
 
@@ -72,6 +73,7 @@ exports.createResolveFn = function(options: ResolveOptions): ResolveFn {
     assetExts,
     extraNodeModules,
     transformedFiles,
+    sourceExts,
   } = options;
   const files = Object.keys(transformedFiles);
   function getTransformedFile(path) {
@@ -93,7 +95,7 @@ exports.createResolveFn = function(options: ResolveOptions): ResolveFn {
     getTransformedFile,
   );
   const hasteMap = new HasteMap({
-    extensions: ['js', 'json'],
+    extensions: sourceExts,
     files,
     helpers,
     moduleCache,
@@ -119,6 +121,7 @@ exports.createResolveFn = function(options: ResolveOptions): ResolveFn {
         platform,
         platforms,
         preferNativePlatform: true,
+        sourceExts,
       });
     }
 
diff --git a/packager/src/Resolver/index.js b/packager/src/Resolver/index.js
index 110913966..ea2bd23cb 100644
--- a/packager/src/Resolver/index.js
+++ b/packager/src/Resolver/index.js
@@ -46,6 +46,7 @@ type Options = {|
   +providesModuleNodeModules: Array<string>,
   +reporter: Reporter,
   +resetCache: boolean,
+  +sourceExts: Array<string>,
   +transformCode: TransformCode,
   +watch: boolean,
 |};
@@ -67,7 +68,6 @@ class Resolver {
   static async load(opts: Options): Promise<Resolver> {
     const depGraphOpts = Object.assign(Object.create(opts), {
       assetDependencies: ['react-native/Libraries/Image/AssetRegistry'],
-      extensions: ['js', 'json'],
       forceNodeFilesystemAPI: false,
       ignoreFilePath(filepath) {
         return filepath.indexOf('__tests__') !== -1 ||
diff --git a/packager/src/Server/index.js b/packager/src/Server/index.js
index b450506c0..4344cd287 100644
--- a/packager/src/Server/index.js
+++ b/packager/src/Server/index.js
@@ -74,6 +74,7 @@ type Options = {
   reporter: Reporter,
   resetCache?: boolean,
   silent?: boolean,
+  +sourceExts: ?Array<string>,
   transformModulePath?: string,
   transformTimeoutInterval?: number,
   watch?: boolean,
@@ -129,6 +130,7 @@ class Server {
     reporter: Reporter,
     resetCache: boolean,
     silent: boolean,
+    +sourceExts: Array<string>,
     transformModulePath: void | string,
     transformTimeoutInterval: ?number,
     watch: boolean,
@@ -166,6 +168,7 @@ class Server {
       reporter: options.reporter,
       resetCache: options.resetCache || false,
       silent: options.silent || false,
+      sourceExts: options.sourceExts || defaults.sourceExts,
       transformModulePath: options.transformModulePath,
       transformTimeoutInterval: options.transformTimeoutInterval,
       watch: options.watch || false,
diff --git a/packager/src/node-haste/DependencyGraph/ResolutionRequest.js b/packager/src/node-haste/DependencyGraph/ResolutionRequest.js
index 6e2a910c3..170d8e05d 100644
--- a/packager/src/node-haste/DependencyGraph/ResolutionRequest.js
+++ b/packager/src/node-haste/DependencyGraph/ResolutionRequest.js
@@ -71,6 +71,7 @@ type Options<TModule, TPackage> = {|
   +platform: ?string,
   +platforms: Set<string>,
   +preferNativePlatform: boolean,
+  +sourceExts: Array<string>,
 |};
 
 /**
@@ -528,22 +529,39 @@ class ResolutionRequest<TModule: Moduleish, TPackage: Packageish> {
     let file;
     if (this._options.hasteFS.exists(potentialModulePath)) {
       file = potentialModulePath;
-    } else if (this._options.platform != null &&
-               this._options.hasteFS.exists(potentialModulePath + '.' + this._options.platform + '.js')) {
-      file = potentialModulePath + '.' + this._options.platform + '.js';
-    } else if (this._preferNativePlatform &&
-               this._options.hasteFS.exists(potentialModulePath + '.native.js')) {
-      file = potentialModulePath + '.native.js';
-    } else if (this._options.hasteFS.exists(potentialModulePath + '.js')) {
-      file = potentialModulePath + '.js';
-    } else if (this._options.hasteFS.exists(potentialModulePath + '.json')) {
-      file = potentialModulePath + '.json';
     } else {
-      throw new UnableToResolveError(
-        fromModule,
-        toModule,
-        `File ${potentialModulePath} doesn't exist`,
-      );
+      const {platform, preferNativePlatform, hasteFS} = this._options;
+      for (let i = 0; i < this._options.sourceExts.length; i++) {
+        const ext = this._options.sourceExts[i];
+        if (platform != null) {
+          const platformSpecificPath = `${potentialModulePath}.${platform}.${ext}`;
+          if (hasteFS.exists(platformSpecificPath)) {
+            file = platformSpecificPath;
+            break;
+          }
+        }
+        if (preferNativePlatform) {
+          const nativeSpecificPath = `${potentialModulePath}.native.${ext}`;
+          if (hasteFS.exists(nativeSpecificPath)) {
+            file = nativeSpecificPath;
+            break;
+          }
+        }
+        const genericPath = `${potentialModulePath}.${ext}`;
+        if (hasteFS.exists(genericPath)) {
+          file = genericPath;
+          break;
+        }
+      }
+
+      if (file == null) {
+        throw new UnableToResolveError(
+          fromModule,
+          toModule,
+          `File ${potentialModulePath} doesn't exist`,
+        );
+      }
+
     }
 
     return this._options.moduleCache.getModule(file);
diff --git a/packager/src/node-haste/__tests__/DependencyGraph-test.js b/packager/src/node-haste/__tests__/DependencyGraph-test.js
index a90ed9907..857849ec0 100644
--- a/packager/src/node-haste/__tests__/DependencyGraph-test.js
+++ b/packager/src/node-haste/__tests__/DependencyGraph-test.js
@@ -40,7 +40,7 @@ describe('DependencyGraph', function() {
   let emptyTransformOptions;
 
   function getOrderedDependenciesAsJSON(dgraphPromise, entryPath, platform, recursive = true) {
-    return dgraphPromise
+    return Promise.resolve(dgraphPromise)
       .then(dgraph => dgraph.getDependencies({
         entryPath,
         options: emptyTransformOptions,
@@ -72,7 +72,6 @@ describe('DependencyGraph', function() {
     emptyTransformOptions = {transformer: {transform: {}}};
     defaults = {
       assetExts: ['png', 'jpg'],
-      extensions: ['js', 'json'],
       forceNodeFilesystemAPI: true,
       providesModuleNodeModules: [
         'haste-fbjs',
@@ -96,6 +95,7 @@ describe('DependencyGraph', function() {
       },
       getTransformCacheKey: () => 'abcdef',
       reporter: require('../../lib/reporting').nullReporter,
+      sourceExts: ['js', 'json'],
       watch: true,
     };
   });
@@ -5250,7 +5250,7 @@ describe('DependencyGraph', function() {
       var dgraph = DependencyGraph.load({
         ...defaults,
         roots: [root],
-        extensions: ['jsx', 'coffee'],
+        sourceExts: ['jsx', 'coffee'],
       });
 
       return dgraph
@@ -5284,6 +5284,80 @@ describe('DependencyGraph', function() {
           ]);
         });
     });
+
+    it('supports custom file extensions with relative paths', async () => {
+      const root = '/root';
+      setMockFileSystem({
+        'root': {
+          'index.jsx': [
+            'require("./a")',
+          ].join('\n'),
+          'a.coffee': [
+          ].join('\n'),
+          'X.js': '',
+        },
+      });
+
+      const dgraph = await DependencyGraph.load({
+        ...defaults,
+        roots: [root],
+        sourceExts: ['jsx', 'coffee'],
+      });
+      const files = await dgraph.matchFilesByPattern('.*');
+      expect(files).toEqual([
+        '/root/index.jsx', '/root/a.coffee',
+      ]);
+
+      const deps = await getOrderedDependenciesAsJSON(dgraph, '/root/index.jsx');
+      expect(deps).toEqual([
+        {
+          dependencies: ['./a'],
+          id: '/root/index.jsx',
+          isAsset: false,
+          isJSON: false,
+          isPolyfill: false,
+          path: '/root/index.jsx',
+          resolution: undefined,
+        },
+        {
+          dependencies: [],
+          id: '/root/a.coffee',
+          isAsset: false,
+          isJSON: false,
+          isPolyfill: false,
+          path: '/root/a.coffee',
+          resolution: undefined,
+        },
+      ]);
+    });
+
+    it('does not include extensions that are not specified explicitely', async () => {
+      const root = '/root';
+      setMockFileSystem({
+        'root': {
+          'index.jsx': [
+            'require("./a")',
+          ].join('\n'),
+          'a.coffee': [
+          ].join('\n'),
+          'X.js': '',
+        },
+      });
+
+      const dgraph = await DependencyGraph.load({
+        ...defaults,
+        roots: [root],
+      });
+      const files = await dgraph.matchFilesByPattern('.*');
+      expect(files).toEqual(['/root/X.js']);
+
+      try {
+        await getOrderedDependenciesAsJSON(dgraph, '/root/index.jsx');
+        throw Error('should not reach this line');
+      } catch (error) {
+        expect(error.type).toEqual('UnableToResolveError');
+      }
+    });
   });
 
   describe('Progress updates', () => {
diff --git a/packager/src/node-haste/index.js b/packager/src/node-haste/index.js
index 0633d23d5..b950f2b1a 100644
--- a/packager/src/node-haste/index.js
+++ b/packager/src/node-haste/index.js
@@ -51,7 +51,6 @@ import type {HasteFS} from './types';
 type Options = {|
   +assetDependencies: Array<string>,
   +assetExts: Array<string>,
-  +extensions: Array<string>,
   +extraNodeModules: ?{},
   +forceNodeFilesystemAPI: boolean,
   +getTransformCacheKey: GetTransformCacheKey,
@@ -65,6 +64,7 @@ type Options = {|
   +reporter: Reporter,
   +resetCache: boolean,
   +roots: Array<string>,
+  +sourceExts: Array<string>,
   +transformCode: TransformCode,
   +useWatchman: boolean,
   +watch: boolean,
@@ -103,7 +103,7 @@ class DependencyGraph extends EventEmitter {
 
   static _createHaste(opts: Options): JestHasteMap {
     return new JestHasteMap({
-      extensions: opts.extensions.concat(opts.assetExts),
+      extensions: opts.sourceExts.concat(opts.assetExts),
       forceNodeFilesystemAPI: opts.forceNodeFilesystemAPI,
       ignorePattern: {test: opts.ignoreFilePath},
       maxWorkers: opts.maxWorkerCount,
@@ -234,6 +234,7 @@ class DependencyGraph extends EventEmitter {
       platform,
       platforms: this._opts.platforms,
       preferNativePlatform: this._opts.preferNativePlatform,
+      sourceExts: this._opts.sourceExts,
     });
 
     const response = new ResolutionResponse(options);