diff --git a/lib/6to5/transformer.js b/lib/6to5/transformer.js
index 3455588d07..78bc05a342 100644
--- a/lib/6to5/transformer.js
+++ b/lib/6to5/transformer.js
@@ -66,12 +66,15 @@ Transformer.prototype.transform = function (file) {
 
 Transformer.prototype.canRun = function (file) {
   var opts = file.opts;
+  var key  = this.key;
 
   var blacklist = opts.blacklist;
-  if (blacklist.length && _.contains(blacklist, this.key)) return false;
+  if (blacklist.length && _.contains(blacklist, key)) return false;
 
-  var whitelist = opts.whitelist;
-  if (whitelist.length && !_.contains(whitelist, this.key)) return false;
+  if (key[0] !== "_") {
+    var whitelist = opts.whitelist;
+    if (whitelist.length && !_.contains(whitelist, key)) return false;
+  }
 
   return true;
 };