diff --git a/sys/dev/rtwn/rtl8812a/usb/r12au_attach.c b/sys/dev/rtwn/rtl8812a/usb/r12au_attach.c
--- a/sys/dev/rtwn/rtl8812a/usb/r12au_attach.c
+++ b/sys/dev/rtwn/rtl8812a/usb/r12au_attach.c
@@ -173,6 +173,11 @@
 				 IEEE80211_HTC_TXLDPC;
 	}
 
+	ic->ic_htcaps |=
+	    IEEE80211_HTCAP_CHWIDTH40 /* 40 MHz channel width */
+	    | IEEE80211_HTCAP_SHORTGI40 /* short GI in 40MHz */
+	;
+
 	/* TODO: STBC, VHT etc */
 }
 
@@ -291,5 +296,7 @@
 	sc->ntxchains			= 2;
 	sc->nrxchains			= 2;
 
+	sc->sc_ht40			= 1;
+
 	r12a_attach_private(sc);
 }
diff --git a/sys/dev/rtwn/rtl8821a/usb/r21au_attach.c b/sys/dev/rtwn/rtl8821a/usb/r21au_attach.c
--- a/sys/dev/rtwn/rtl8821a/usb/r21au_attach.c
+++ b/sys/dev/rtwn/rtl8821a/usb/r21au_attach.c
@@ -158,6 +158,11 @@
 	if (rs->rs_radar != 0)
 		ic->ic_caps |= IEEE80211_C_DFS;
 
+	ic->ic_htcaps |=
+	    IEEE80211_HTCAP_CHWIDTH40 /* 40 MHz channel width */
+	    | IEEE80211_HTCAP_SHORTGI40 /* short GI in 40MHz */
+	    ;
+
 	/* TODO: VHT */
 }
 
@@ -277,5 +282,7 @@
 	sc->ntxchains			= 1;
 	sc->nrxchains			= 1;
 
+	sc->sc_ht40			= 1;
+
 	r21a_attach_private(sc);
 }