* Unmerged path sys/amd64/conf/SABRINA
diff --git a/sys/dev/iwn/if_iwn.c b/sys/dev/iwn/if_iwn.c
index 7fc013704253..4f755829d4fa 100644
--- a/sys/dev/iwn/if_iwn.c
+++ b/sys/dev/iwn/if_iwn.c
@@ -4587,12 +4587,23 @@ iwn_tx_data(struct iwn_softc *sc, struct mbuf *m, struct ieee80211_node *ni)
 	 * anyway ourselves (and should stub out / warn / etc.)
 	 */
 
+	/*
+	 * Ok, this is a bit "fun" and could do with some cleanup.
+	 * 'ac' here is (mostly) the AC, not TID.  It's actually used
+	 * as the destination txq.
+	 *
+	 * For A-MPDU enabled queues, 'ac' becomes the private queue
+	 * allocated for this TID.  However, ni_tx_ampdu[] is now per
+	 * TID, not per AC.  So a little twisty logic is done here.
+	 */
 	ac = M_WME_GETAC(m);
 	if (m->m_flags & M_AMPDU_MPDU) {
-		struct ieee80211_tx_ampdu *tap = &ni->ni_tx_ampdu[ac];
+		struct ieee80211_tx_ampdu *tap =
+		    &ni->ni_tx_ampdu[WME_AC_TO_TID(ac)];
 
-		if (!IEEE80211_AMPDU_RUNNING(tap))
+		if (!IEEE80211_AMPDU_RUNNING(tap)) {
 			return (EINVAL);
+		}
 
 		ac = *(int *)tap->txa_private;
 	}