diff --git a/lib/async.js b/lib/async.js
index a13f83520..61184ef91 100755
--- a/lib/async.js
+++ b/lib/async.js
@@ -121,6 +121,7 @@
             return callback();
         }
         var completed = 0;
+        var arr_length = arr.length;
         _each(arr, function (x) {
             iterator(x, only_once(done) );
         });
@@ -131,7 +132,7 @@
           }
           else {
               completed += 1;
-              if (completed >= arr.length) {
+              if (completed >= arr_length) {
                   callback();
               }
           }