diff --git a/lib/6to5/transformation/templates/async-to-generator.js b/lib/6to5/transformation/templates/async-to-generator.js
index cb14a12231..3d7b145184 100644
--- a/lib/6to5/transformation/templates/async-to-generator.js
+++ b/lib/6to5/transformation/templates/async-to-generator.js
@@ -3,12 +3,12 @@
     var gen = fn.apply(this, arguments);
 
     return new Promise(function (resolve, reject) {
-      var callNext = step.bind(gen.next);
-      var callThrow = step.bind(gen.throw);
+      var callNext = step.bind(null, "next");
+      var callThrow = step.bind(null, "throw");
 
-      function step(arg) {
+      function step(key, arg) {
         try {
-          var info = this(arg);
+          var info = gen[key](arg);
           var value = info.value;
         } catch (error) {
           reject(error);