diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 3a278c94e1..a57cae7a73 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -13,10 +13,10 @@ require.extensions[".es6"] = function (m, filename) {
   }
 
   var result = node.transformFileSync(filename, {
-    sourceMapObject: true
+    sourceMap: true
   });
 
-  //maps[filename] = result.map;
+  maps[filename] = result.map;
 
   m._compile(result.code, filename);
 };