diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index 118af4b42a..1781ffca9d 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -7,16 +7,22 @@ var _        = require("lodash");
 function Scope(parent, block) {
   this.parent = parent;
   this.block  = block;
-  this.ids    = block._scopeIds = block._scopeIds || Scope.getIds(block);
+  this.ids    = this.getIds();
+
+  this.getIds();
 }
 
-Scope.getIds = function (block) {
-  var ids = {};
+Scope.prototype.getIds = function () {
+  var block = this.block;
+  if (block._scopeIds) return block._scopeIds;
+
+  var self = this;
+  var ids  = block._scopeIds = {};
 
   if (t.isBlockStatement(block)) {
     _.each(block.body, function (node) {
       if (t.isVariableDeclaration(node) && node.kind !== "var") {
-        _.merge(ids, t.getIds(node, true));
+        self.add(node, ids);
       }
     });
   } else if (t.isProgram(block) || t.isFunction(block)) {
@@ -26,7 +32,7 @@ Scope.getIds = function (block) {
       }
 
       if (t.isDeclaration(node)) {
-        _.merge(ids, t.getIds(node, true));
+        self.add(node, ids);
       } else if (t.isFunction(node)) {
         return false;
       }
@@ -35,13 +41,17 @@ Scope.getIds = function (block) {
 
   if (t.isFunction(block)) {
     _.each(block.params, function (param) {
-      _.merge(ids, t.getIds(param, true));
+      self.add(param, ids);
     });
   }
 
   return ids;
 };
 
+Scope.prototype.add = function (node, ids) {
+  _.merge(ids || this.ids, t.getIds(node, true));
+};
+
 Scope.prototype.get = function (id) {
   return id && (this.getOwn(id) || this.parentGet(id));
 };