diff --git a/lib/6to5/transformation/transformers/default-parameters.js b/lib/6to5/transformation/transformers/default-parameters.js
index 8e02a2a865..5a850e42d8 100644
--- a/lib/6to5/transformation/transformers/default-parameters.js
+++ b/lib/6to5/transformation/transformers/default-parameters.js
@@ -3,7 +3,7 @@ var t    = require("../../types");
 var _    = require("lodash");
 
 exports.Function = function (node) {
-  if (!node.defaults.length) return;
+  if (!node.defaults || !node.defaults.length) return;
   t.ensureBlock(node);
 
   _.each(node.defaults, function (def, i) {