diff --git a/src/Monitoring/ThreadUpdater.coffee b/src/Monitoring/ThreadUpdater.coffee
index 067adc028..0fae7a339 100755
--- a/src/Monitoring/ThreadUpdater.coffee
+++ b/src/Monitoring/ThreadUpdater.coffee
@@ -316,7 +316,7 @@ ThreadUpdater =
     else
       ThreadUpdater.set 'status', "+#{count}", 'new'
       ThreadUpdater.outdateCount = 0
-      if Conf['Beep'] and d.hidden and Unread.posts and !Unread.posts.length
+      if Conf['Beep'] and d.hidden and Unread.posts and !Unread.posts.size
         unless ThreadUpdater.audio
           ThreadUpdater.audio = $.el 'audio', src: ThreadUpdater.beep
         ThreadUpdater.audio.play()