diff --git a/sys/net80211/ieee80211_radiotap.h b/sys/net80211/ieee80211_radiotap.h
index bee1c633b53..1babd80d4b0 100644
--- a/sys/net80211/ieee80211_radiotap.h
+++ b/sys/net80211/ieee80211_radiotap.h
@@ -433,6 +433,7 @@ struct ieee80211_radiotap_he {
 #define	IEEE80211_RADIOTAP_HE_DATA4_TB_SPTL_REUSE4		0xF000
 
 #define	IEEE80211_RADIOTAP_HE_DATA5_LTF_SIZE			0x00C0
+#define	IEEE80211_RADIOTAP_HE_DATA5_LTF_SIZE_UNKNOWN		0x0
 #define	IEEE80211_RADIOTAP_HE_DATA5_LTF_SIZE_1X			0x1
 #define	IEEE80211_RADIOTAP_HE_DATA5_LTF_SIZE_2X			0x2
 #define	IEEE80211_RADIOTAP_HE_DATA5_LTF_SIZE_4X			0x3