diff --git a/lib/scheduler/manager.rb b/lib/scheduler/manager.rb
index 0bc8dd70e1..b1449973a1 100644
--- a/lib/scheduler/manager.rb
+++ b/lib/scheduler/manager.rb
@@ -45,7 +45,7 @@ module Scheduler
       end
 
       def wait_till_done
-        while !@queue.empty? && !@queue.num_waiting > 0
+        while !@queue.empty? && !(@queue.num_waiting > 0)
           sleep 0.001
         end
       end