diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index cb45f4d2c6..d20b5aba56 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -21,15 +21,19 @@ function Scope(block, parent) {
   this.references = this.getReferences();
 }
 
+Scope.add = function (node, references) {
+  if (!node) return;
+  _.merge(references, t.getIds(node, true));
+};
+
 Scope.prototype.getReferences = function () {
   var block = this.block;
   if (block._scopeReferences) return block._scopeReferences;
 
-  var self       = this;
   var references = block._scopeReferences = {};
 
   var add = function (node) {
-    self.add(node, references);
+    Scope.add(node, references);
   };
 
   // ForStatement - left, init
@@ -116,9 +120,8 @@ Scope.prototype.push = function (name, id, init) {
   }
 };
 
-Scope.prototype.add = function (node, references) {
-  if (!node) return;
-  _.merge(references || this.references, t.getIds(node, true));
+Scope.prototype.add = function (node) {
+  Scope.add(node, this.references);
 };
 
 Scope.prototype.get = function (id) {