diff --git a/lib/6to5/transformation/transformers/es6-default-parameters.js b/lib/6to5/transformation/transformers/es6-default-parameters.js
index ac7a41ff38..b369678daa 100644
--- a/lib/6to5/transformation/transformers/es6-default-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-default-parameters.js
@@ -11,8 +11,6 @@ exports.Function = function (node, parent, file, scope) {
   });
 
   var iife = false;
-  var i;
-  var def;
 
   var checkTDZ = function (ids) {
     var check = function (node, parent) {
@@ -31,8 +29,8 @@ exports.Function = function (node, parent, file, scope) {
     traverse(def, { enter: check });
   };
 
-  for (i = 0; i < node.defaults.length; i++) {
-    def = node.defaults[i];
+  for (var i = 0; i < node.defaults.length; i++) {
+    var def = node.defaults[i];
     if (!def) continue;
 
     var param = node.params[i];
@@ -40,8 +38,8 @@ exports.Function = function (node, parent, file, scope) {
     // temporal dead zone check - here we prevent accessing of params that
     // are to the right - ie. uninitialized parameters
     var rightIds = ids.slice(i);
-    for (i = 0; i < rightIds.length; i++) {
-      checkTDZ(rightIds[i]);
+    for (var i2 = 0; i2 < rightIds.length; i2++) {
+      checkTDZ(rightIds[i2]);
     }
 
     // we're accessing a variable that's already defined within this function