diff --git a/lib/6to5/types/index.js b/lib/6to5/types/index.js
index 4e960efffb..51752c3961 100644
--- a/lib/6to5/types/index.js
+++ b/lib/6to5/types/index.js
@@ -490,7 +490,11 @@ t.toBlock = function (node, parent) {
 };
 
 /**
- * Description
+ * Return a list of identifiers that will be assigned
+ * as a result of runtime evaluation.
+ *
+ * If an identifier is passed as `node` instead of a
+ * declaration then it's assumed to be an assignable.
  *
  * @param {Object} node
  * @param {Boolean} [map]
@@ -499,15 +503,15 @@ t.toBlock = function (node, parent) {
  */
 
 t.getIds = function (node, map, ignoreTypes) {
-  ignoreTypes = ignoreTypes || [];
-
   var search = [].concat(node);
   var ids    = object();
 
   while (search.length) {
     var id = search.shift();
     if (!id) continue;
-    if (_.contains(ignoreTypes, id.type)) continue;
+
+    // blacklist types
+    if (ignoreTypes && ignoreTypes.indexOf(id.type) >= 0) continue;
 
     var nodeKeys = t.getIds.nodes[id.type];
     var arrKeys  = t.getIds.arrays[id.type];