diff --git a/lib/browser/object-sync-client.coffee b/lib/browser/object-sync-client.coffee
index dbfa859..01e57b4 100644
--- a/lib/browser/object-sync-client.coffee
+++ b/lib/browser/object-sync-client.coffee
@@ -5,7 +5,7 @@ console.trace or= ->
 console.dir or= ->
 
 if not Array.indexOf
-  Array.prototype.indexOf = (obj) ->
+  Array::indexOf = (obj) ->
     for i in [0..@length]
       if this[i] is obj
         return i
@@ -239,4 +239,4 @@ class ObjectSync extends EventEmitter
       fn.apply @, args
     delete @_req_callbacks[req_id]
     
-window.ObjectSync = ObjectSync
\ No newline at end of file
+window.ObjectSync = ObjectSync