diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 3643024506..b36bd09cd8 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -98,5 +98,10 @@ module.exports = function (opts) {
 
   if (opts.cache === false) cache = null;
 
+  delete opts.extensions;
+  delete opts.ignore;
+  delete opts.cache;
+  delete opts.only;
+
   _.extend(transformOpts, opts);
 };