diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 1ccadaec56..6a5b98fefc 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -97,7 +97,7 @@ module.exports = function (opts) {
   // normalise options
   opts = opts || {};
   if (_.isRegExp(opts)) opts = { ignore: opts };
-  opts.ignore = opts.ignore || opts.ignoreRegex;
+  if (opts.ignoreRegex != null) opts.ignore = opts.ignoreRegex;
 
   if (opts.only != null) onlyRegex = opts.only;
   if (opts.ignore != null) ignoreRegex = opts.ignore;