diff --git a/lib/6to5/transformation/helpers/replace-supers.js b/lib/6to5/transformation/helpers/replace-supers.js
index 4ec70cf6b5..2403e878cb 100644
--- a/lib/6to5/transformation/helpers/replace-supers.js
+++ b/lib/6to5/transformation/helpers/replace-supers.js
@@ -152,7 +152,7 @@ ReplaceSupers.prototype.getThisReference = function () {
     return this.topLevelThisReference;
   } else {
     var ref = this.topLevelThisReference = this.file.generateUidIdentifier("this");
-    this.methodNode.body.body.unshift(t.variableDeclaration("var", [
+    this.methodNode.value.body.body.unshift(t.variableDeclaration("var", [
       t.variableDeclarator(this.topLevelThisReference, t.thisExpression())
     ]));
     return ref;