diff --git a/check_mysql_slave.py b/check_mysql_slave.py
index d04f165..ce90b91 100755
--- a/check_mysql_slave.py
+++ b/check_mysql_slave.py
@@ -73,8 +73,8 @@ def main(args):
         if exit_code == nagios.STATE_OK:
             # Only replication delay if everything else is healthy.
             if not slave_status['Seconds_Behind_Master']:
-                print("UNKNOWN - Could not retrieve Seconds_Behind_Master")
-                sys.exit(nagios.STATE_UNKNOWN)
+                quit_check('Slave is not configured for delay', nagios.STATE_CRIT)
+
             replication_delay = try_int(slave_status['Seconds_Behind_Master'])
 
             if args.target_delay: