diff --git a/sys/net80211/ieee80211.h b/sys/net80211/ieee80211.h
--- a/sys/net80211/ieee80211.h
+++ b/sys/net80211/ieee80211.h
@@ -931,6 +931,7 @@
 	IEEE80211_VHT_MCS_NOT_SUPPORTED		= 3	/* not supported */
 };
 
+/* 802.11ac-2013, 8.4.2.160.3 Supported VHT-MCS and NSS Set field */
 struct ieee80211_vht_mcs_info {
 	uint16_t rx_mcs_map;
 	uint16_t rx_highest;