--- openflow-2014-01-14.h	2015-07-23 09:54:17.604479381 -0700
+++ openflow-2013-09-09.h	2015-07-23 09:54:17.608479381 -0700
@@ -2048,7 +2048,7 @@
      * The reply body is an array of struct ofp_queue_desc. */
     OFPMP_QUEUE_DESC = 15,
 
-    /* Flow monitors.
+    /* Flow monitors. Reply may be an asynchronous message.
      * The request body is struct ofp_flow_monitor_request.
      * The reply body is an array of struct ofp_flow_update_header. */
     OFPMP_FLOW_MONITOR = 16,