diff --git a/local-cli/bundle/output/meta.js b/local-cli/bundle/output/meta.js
index 2bfc3a670..4c110ada7 100644
--- a/local-cli/bundle/output/meta.js
+++ b/local-cli/bundle/output/meta.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';
 
@@ -19,12 +21,16 @@ const constantFor = encoding =>
   isUTF8(encoding) ? 2 :
   /^(?:utf-?16(?:le)?|ucs-?2)$/.test(encoding) ? 3 : 0;
 
-module.exports = function(code, encoding) {
+module.exports = function(
+  code: string,
+  encoding: 'ascii' | 'utf8' | 'utf16le' = 'utf8',
+): Buffer {
   const hash = crypto.createHash('sha1');
-  hash.update(code, encoding);
-  const digest = hash.digest('binary');
-  const signature = Buffer.alloc ? Buffer.alloc(digest.length + 1) : new Buffer(digest.length + 1); // remove the new Buffer call when RN drops support for Node 4
-  signature.write(digest, 'binary');
+  // remove `new Buffer` calls when RN drops support for Node 4
+  hash.update(Buffer.from ? Buffer.from(code, encoding) : new Buffer(code, encoding));
+  const digest = hash.digest();
+  const signature = Buffer.alloc ? Buffer.alloc(digest.length + 1) : new Buffer(digest.length + 1);
+  digest.copy(signature);
   signature.writeUInt8(
     constantFor(tryAsciiPromotion(code, encoding)),
     signature.length - 1);