diff --git a/lib/6to5/transformation/modules/system.js b/lib/6to5/transformation/modules/system.js
index 8a24bca43f..e7a320618b 100644
--- a/lib/6to5/transformation/modules/system.js
+++ b/lib/6to5/transformation/modules/system.js
@@ -80,7 +80,7 @@ SystemFormatter.prototype.transform = function (ast) {
 
   // hoist up function declarations for circular references
   traverse(program, {
-    enter: function (node, parent) {
+    enter: function (node) {
       if (t.isFunction(node)) this.stop();
 
       if (t.isFunctionDeclaration(node) || node._blockHoist) {