diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 9dbd1bf589..30fc5e5a82 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -72,7 +72,8 @@ var loader = function (m, filename) {
   var result = to5.transformFileSync(filename, {
     whitelist: whitelist,
     blacklist: blacklist,
-    sourceMap: true
+    sourceMap: true,
+    modules:   "commonInterop"
   });
 
   maps[filename] = result.map;