--- openflow-2011-11-22.h	2015-07-23 09:54:16.856479350 -0700
+++ openflow-2011-11-23.h	2015-07-23 09:54:16.860479350 -0700
@@ -481,7 +481,7 @@
  * This field is usually not available in a regular match and only available
  * in ofp_packet_in messages when it's different from OXM_OF_IN_PORT.
  *
- * Prereqs: None.
+ * Prereqs: OXM_OF_IN_PORT must be present.
  *
  * Format: 32-bit integer in network byte order.
  *