diff --git a/local-cli/bundle/output/bundle.js b/local-cli/bundle/output/bundle.js
index 2cbb7be08..54eab0587 100644
--- a/local-cli/bundle/output/bundle.js
+++ b/local-cli/bundle/output/bundle.js
@@ -9,7 +9,7 @@
 'use strict';
 
 const Promise = require('promise');
-const hash = require('./hash');
+const meta = require('./meta');
 const writeFile = require('./writeFile');
 
 function buildBundle(packagerClient, requestOptions) {
@@ -37,15 +37,20 @@ function saveBundleAndMap(bundle, options, log) {
 
   log('Writing bundle output to:', bundleOutput);
 
-  const code = hash.appendToString(codeWithMap.code, encoding);
+  const {code} = codeWithMap;
   const writeBundle = writeFile(bundleOutput, code, encoding);
-  writeBundle.then(() => log('Done writing bundle output'));
+  const writeMetadata = writeFile(
+    bundleOutput + '.meta',
+    meta(code, encoding),
+    'binary');
+  Promise.all([writeBundle, writeMetadata])
+    .then(() => log('Done writing bundle output'));
 
   if (sourcemapOutput) {
     log('Writing sourcemap output to:', sourcemapOutput);
     const writeMap = writeFile(sourcemapOutput, codeWithMap.map, null);
     writeMap.then(() => log('Done writing sourcemap output'));
-    return Promise.all([writeBundle, writeMap]);
+    return Promise.all([writeBundle, writeMetadata, writeMap]);
   } else {
     return writeBundle;
   }
diff --git a/local-cli/bundle/output/hash.js b/local-cli/bundle/output/meta.js
similarity index 56%
rename from local-cli/bundle/output/hash.js
rename to local-cli/bundle/output/meta.js
index c02c95746..d7f837a0e 100644
--- a/local-cli/bundle/output/hash.js
+++ b/local-cli/bundle/output/meta.js
@@ -10,14 +10,23 @@
 
 const crypto = require('crypto');
 
-const createHash = () => crypto.createHash('sha1');
 const isUTF8 = encoding => /^utf-?8$/i.test(encoding);
 
-exports.appendToString = (string, encoding) => {
-  const hash = createHash();
-  hash.update(string, encoding);
-  encoding = tryAsciiPromotion(string, encoding);
-  return string + formatSignature(encoding, hash);
+const constantFor = encoding =>
+  /^ascii$/i.test(encoding) ? 1 :
+  isUTF8(encoding) ? 2 :
+  /^(?:utf-?16(?:le)?|ucs-?2)$/ ? 3 : 0;
+
+module.exports = function(code, encoding) {
+  const hash = crypto.createHash('sha1');
+  hash.update(code, encoding);
+  const digest = hash.digest('binary');
+  const signature = Buffer(digest.length + 1);
+  signature.write(digest, 'binary');
+  signature.writeUInt8(
+    constantFor(tryAsciiPromotion(code, encoding)),
+    signature.length - 1);
+  return signature;
 };
 
 function tryAsciiPromotion(string, encoding) {
@@ -27,7 +36,3 @@ function tryAsciiPromotion(string, encoding) {
   }
   return 'ascii';
 }
-
-function formatSignature(encoding, hash) {
-  return `/*${encoding}:${hash.digest('hex')}*/`;
-}