diff --git a/lib/6to5/traverse/index.js b/lib/6to5/traverse/index.js
index 42f48f2c29..c74e007c64 100644
--- a/lib/6to5/traverse/index.js
+++ b/lib/6to5/traverse/index.js
@@ -87,6 +87,7 @@ traverse.removeProperties = function (tree) {
   var clear = function (node) {
     delete node.extendedRange;
     delete node._scopeIds;
+    delete node._parent;
     delete node.tokens;
     delete node.range;
     delete node.start;