diff --git a/lib/6to5/transformation/transformers/es6-let-scoping.js b/lib/6to5/transformation/transformers/es6-let-scoping.js
index 9c7d0aeb16..b0e7a4d97b 100644
--- a/lib/6to5/transformation/transformers/es6-let-scoping.js
+++ b/lib/6to5/transformation/transformers/es6-let-scoping.js
@@ -233,7 +233,7 @@ LetScoping.prototype.getInfo = function () {
 
   var declar;
 
-  for (var i in opts.declarators) {
+  for (var i = 0; i < opts.declarators.length; i++) {
     declar = opts.declarators[i];
     opts.declarators.push(declar);