diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index 4425c28036..99551e5174 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -37,6 +37,21 @@ exports.list = function (val) {
   return val ? val.split(",") : [];
 };
 
+exports.regexify = function (val) {
+  if (!val) return new RegExp;
+  if (_.isArray(val)) val = val.join("|");
+  if (_.isString(val)) return new RegExp(val || "");
+  if (_.isRegExp(val)) return val;
+  throw new TypeError("illegal type for regexify");
+};
+
+exports.arrayify = function (val) {
+  if (!val) return [];
+  if (_.isString(val)) return exports.list(val);
+  if (_.isArray(val)) return val;
+  throw new TypeError("illegal type for arrayify");
+};
+
 exports.getUid = function (parent, file) {
   var node;