diff --git a/sys/netproto/802_11/wlan/ieee80211_crypto.c b/sys/netproto/802_11/wlan/ieee80211_crypto.c
--- a/sys/netproto/802_11/wlan/ieee80211_crypto.c
+++ b/sys/netproto/802_11/wlan/ieee80211_crypto.c
@@ -586,7 +586,7 @@
 {
 #define	IEEE80211_WEP_HDRLEN	(IEEE80211_WEP_IVLEN + IEEE80211_WEP_KIDLEN)
 #define	IEEE80211_WEP_MINLEN \
-	(sizeof(struct ieee80211_frame) + \
+	(hdrlen + \
 	IEEE80211_WEP_HDRLEN + IEEE80211_WEP_CRCLEN)
 	struct ieee80211vap *vap = ni->ni_vap;
 	struct ieee80211_key *k;