diff --git a/platform/chromium/polyfill.js b/platform/chromium/polyfill.js
index d39d2d39c..a21e130e1 100644
--- a/platform/chromium/polyfill.js
+++ b/platform/chromium/polyfill.js
@@ -68,6 +68,7 @@ var objectAssign = Object.assign || function(target, source) {
         key = keys[i];
         target[key] = source[key];
     }
+    return target;
 };
 
 /******************************************************************************/
diff --git a/platform/firefox/polyfill.js b/platform/firefox/polyfill.js
index ca2b44056..6daf9fd46 100644
--- a/platform/firefox/polyfill.js
+++ b/platform/firefox/polyfill.js
@@ -37,6 +37,7 @@ var objectAssign = Object.assign || function(target, source) {
         key = keys[i];
         target[key] = source[key];
     }
+    return target;
 };
 
 /******************************************************************************/