diff --git a/lib/6to5/transformation/transformers/es6-default-parameters.js b/lib/6to5/transformation/transformers/es6-default-parameters.js
index db82d8e2d4..674c1096dc 100644
--- a/lib/6to5/transformation/transformers/es6-default-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-default-parameters.js
@@ -45,7 +45,7 @@ exports.Function = function (node, parent, file, scope) {
     }
 
     // we're accessing a variable that's already defined within this function
-    var has = scope.get(param.name);
+    var has = scope.get(param.name, true);
     if (has && node.params.indexOf(has) < 0) {
       iife = true;
     }