diff --git a/local-cli/bundle/filterPlatformAssetScales.js b/local-cli/bundle/filterPlatformAssetScales.js
index 75e07edc0..d9e8daa2e 100644
--- a/local-cli/bundle/filterPlatformAssetScales.js
+++ b/local-cli/bundle/filterPlatformAssetScales.js
@@ -5,23 +5,30 @@
  * 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
+ * @format
  */
+
 'use strict';
 
 const ALLOWED_SCALES = {
   ios: [1, 2, 3],
 };
 
-function filterPlatformAssetScales(platform, scales) {
+function filterPlatformAssetScales(
+  platform: string,
+  scales: $ReadOnlyArray<number>,
+): $ReadOnlyArray<number> {
   const whitelist = ALLOWED_SCALES[platform];
   if (!whitelist) {
     return scales;
   }
   const result = scales.filter(scale => whitelist.indexOf(scale) > -1);
   if (result.length === 0 && scales.length > 0) {
-    // No matching scale found, but there are some available. Ideally we don't want to
-    // be in this situation and should throw, but for now as a fallback let's just use
-    // the closest larger image
+    // No matching scale found, but there are some available. Ideally we don't
+    // want to be in this situation and should throw, but for now as a fallback
+    // let's just use the closest larger image
     const maxScale = whitelist[whitelist.length - 1];
     for (const scale of scales) {
       if (scale > maxScale) {