diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index d5b2aacdd9..d2888b199b 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -6,6 +6,7 @@ var SHEBANG_REGEX = /^\#\!.*/;
 
 var transform = require("./transformation/transform");
 var generate  = require("./generation/generator");
+var clone     = require("./helpers/clone");
 var Scope     = require("./traverse/scope");
 var util      = require("./util");
 var t         = require("./types");
@@ -73,7 +74,7 @@ File.validOptions = [
 ];
 
 File.normaliseOptions = function (opts) {
-  opts = _.cloneDeep(opts || {});
+  opts = clone(opts);
 
   for (var key in opts) {
     if (File.validOptions.indexOf(key) < 0) {
diff --git a/lib/6to5/helpers/clone.js b/lib/6to5/helpers/clone.js
new file mode 100644
index 0000000000..a00125e8c7
--- /dev/null
+++ b/lib/6to5/helpers/clone.js
@@ -0,0 +1,10 @@
+module.exports = function cloneDeep(obj) {
+  var obj2 = {};
+  if (!obj) return obj2;
+
+  for (var key in obj) {
+    obj2[key] = obj[key];
+  }
+
+  return obj2;
+};