diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index 0a06cfa9c8..e698078268 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -38,9 +38,9 @@ exports.list = function (val) {
 };
 
 exports.regexify = function (val) {
-  if (!val) return new RegExp;
+  if (!val) return new RegExp(/.^/);
   if (_.isArray(val)) val = val.join("|");
-  if (_.isString(val)) return new RegExp(val || "");
+  if (_.isString(val)) return new RegExp(val);
   if (_.isRegExp(val)) return val;
   throw new TypeError("illegal type for regexify");
 };