diff --git a/lib/socket.js b/lib/socket.js
index ce6b226285..6bbefd2dfa 100644
--- a/lib/socket.js
+++ b/lib/socket.js
@@ -252,7 +252,7 @@ Socket.prototype.ack = function(id){
  */
 
 Socket.prototype.onack = function(packet){
-  var ack = this.acks[Number(packet.id)];
+  var ack = this.acks[packet.id];
   if ('function' == typeof ack) {
     debug('calling ack %s with %j', packet.id, packet.data);
     ack.apply(this, packet.data);