diff --git a/src/lib/async.html b/src/lib/async.html
index 7cce5d6331..93028937e6 100644
--- a/src/lib/async.html
+++ b/src/lib/async.html
@@ -63,8 +63,8 @@
   }
 };
 
-new (window.MutationObserver || JsMutationObserver)
-  (Polymer.Async._atEndOfMicrotask.bind(Polymer.Async))
-  .observe(Polymer.Async._twiddle, {characterData: true});
+new window.MutationObserver(function() {
+    Polymer.Async._atEndOfMicrotask();
+  }).observe(Polymer.Async._twiddle, {characterData: true});
 
 </script>