diff --git a/lib/system-formats.js b/lib/system-formats.js
index bfcff3cb..251e6e73 100644
--- a/lib/system-formats.js
+++ b/lib/system-formats.js
@@ -161,7 +161,7 @@
     System.instantiate = function(load) {
       var name = load.name || '';
 
-      if (name == 'traceur')
+      if (!load.source || name == 'traceur')
         return systemInstantiate.call(this, load);
 
       var source = load.source;
@@ -242,4 +242,4 @@
     }
   }
 
-})();
\ No newline at end of file
+})();