diff --git a/lib/namespace.js b/lib/namespace.js
index 3c538a77c..e567cd7c9 100644
--- a/lib/namespace.js
+++ b/lib/namespace.js
@@ -184,7 +184,7 @@
 
       case 'ack':
         if (this.acks[packet.ackId]) {
-          this.acks[packet.ackId].apply(this, packet.args);
+          this.acks[packet.ackId](packet.args);
           delete this.acks[packet.ackId];
         }
         break;