diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index d619620ba4..840039b385 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -41,10 +41,6 @@ var loader = function (m, filename) {
   m._compile(result.code, filename);
 };
 
-var addToBlacklist = function (array) {
-  blacklist = _.union(blacklist, array)
-}
-
 var hookExtensions = function (_exts) {
   _.each(exts, function (old, ext) {
     require.extensions[ext] = old;
@@ -70,5 +66,5 @@ module.exports = function (opts) {
 
   if (opts.extensions) hookExtensions(opts.extensions);
 
-  if (opts.blacklist) addToBlacklist(opts.blacklist);
+  if (opts.blacklist) blacklist = opts.blacklist;
 };