diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index 0e1207b023..d8d9c4ba24 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -165,7 +165,7 @@ File.prototype.addCode = function (code) {
 File.prototype.parse = function (code) {
   var self = this;
 
-  this.addCode(code);
+  code = this.addCode(code);
 
   return util.parse(this.opts, code, function (tree) {
     self.transform(tree);