diff --git a/session.inc.php b/session.inc.php
index f110347..0cb663a 100644
--- a/session.inc.php
+++ b/session.inc.php
@@ -277,6 +277,9 @@ class Session
     //create new coroutines and assign them to free devices
     foreach($devices as $device)
     {
+      if(!$device)
+        continue;
+
       if(sizeof($tasks) == 0)
         break;