diff --git a/lib/6to5/transformation/transformers/es6/parameters.default.js b/lib/6to5/transformation/transformers/es6/parameters.default.js
index 9c3d53239d..7e7d9ac5a4 100644
--- a/lib/6to5/transformation/transformers/es6/parameters.default.js
+++ b/lib/6to5/transformation/transformers/es6/parameters.default.js
@@ -9,7 +9,7 @@ exports.check = function (node) {
 
 var hasDefaults = function (node) {
   for (var i = 0; i < node.params.length; i++) {
-    if (t.isAssignmentPattern(node.params[i])) return true;
+    if (!t.isIdentifier(node.params[i])) return true;
   }
   return false;
 };
@@ -54,9 +54,15 @@ exports.Function = function (node, parent, scope, file) {
 
     if (!t.isAssignmentPattern(param)) {
       lastNonDefaultParam = i + 1;
+
+      if (!t.isIdentifier(param)) {
+        scope.traverse(param, iifeVisitor, state);
+      }
+
       if (file.transformers["es6.blockScopingTDZ"].canRun()) {
         pushDefNode(param, t.identifier("undefined"), i);
       }
+
       continue;
     }