diff --git a/lib/resque/pool.rb b/lib/resque/pool.rb
index 1841c6e..d248615 100644
--- a/lib/resque/pool.rb
+++ b/lib/resque/pool.rb
@@ -386,7 +386,7 @@ def quit_excess_workers_for(queues)
     end
 
     def worker_delta_for(queues)
-      config.fetch(queues, 0) - workers.fetch(queues, []).size
+      (config.fetch(queues, 0) || 0) - workers.fetch(queues, []).size
     end
 
     def pids_for(queues)