diff --git a/scst/src/scst_copy_mgr.c b/scst/src/scst_copy_mgr.c
index f882ffd7f..0360a7262 100644
--- a/scst/src/scst_copy_mgr.c
+++ b/scst/src/scst_copy_mgr.c
@@ -2544,6 +2544,8 @@ static unsigned int scst_cm_get_lun(const struct scst_device *dev)
 	}
 	rcu_read_unlock();
 
+	WARN_ON_ONCE(res == SCST_MAX_LUN);
+
 out:
 	TRACE_EXIT_RES(res);
 	return res;