diff --git a/sys/dev/ath/if_ath.c b/sys/dev/ath/if_ath.c
index bff28ee48fd..bc47f87f0a1 100644
--- a/sys/dev/ath/if_ath.c
+++ b/sys/dev/ath/if_ath.c
@@ -636,6 +636,19 @@ ath_attach(u_int16_t devid, struct ath_softc *sc)
 	}
 #endif
 
+	/*
+	 * TODO: enforce that at least this many frames are available
+	 * in the txbuf list before allowing data frames (raw or
+	 * otherwise) to be transmitted.
+	 */
+	sc->sc_txq_data_minfree = 10;
+	/*
+	 * Leave this as default to maintain legacy behaviour.
+	 * Shortening the cabq/mcastq may end up causing some
+	 * undesirable behaviour.
+	 */
+	sc->sc_txq_mcastq_maxdepth = ath_txbuf;
+
 	/*
 	 * Allow the TX and RX chainmasks to be overridden by
 	 * environment variables and/or device.hints.
diff --git a/sys/dev/ath/if_ath_sysctl.c b/sys/dev/ath/if_ath_sysctl.c
index 73439198e71..410b4c6ce68 100644
--- a/sys/dev/ath/if_ath_sysctl.c
+++ b/sys/dev/ath/if_ath_sysctl.c
@@ -605,6 +605,17 @@ ath_sysctlattach(struct ath_softc *sc)
 		"tid_hwq_hi", CTLFLAG_RW, &sc->sc_tid_hwq_hi, 0,
 		"");
 
+#if 0
+	SYSCTL_ADD_INT(ctx, SYSCTL_CHILDREN(tree), OID_AUTO,
+		"txq_data_minfree", CTLFLAG_RW, &sc->sc_txq_data_minfree,
+		0, "Minimum free buffers before adding a data frame"
+		" to the TX queue");
+#endif
+	SYSCTL_ADD_INT(ctx, SYSCTL_CHILDREN(tree), OID_AUTO,
+		"txq_mcastq_maxdepth", CTLFLAG_RW,
+		&sc->sc_txq_mcastq_maxdepth, 0,
+		"Maximum buffer depth for multicast/broadcast frames");
+
 #ifdef IEEE80211_SUPPORT_TDMA
 	if (ath_hal_macversion(ah) > 0x78) {
 		sc->sc_tdmadbaprep = 2;
@@ -885,7 +896,10 @@ ath_sysctl_stats_attach(struct ath_softc *sc)
 	    &sc->sc_stats.ast_rx_intr, 0, "RX interrupts");
 	SYSCTL_ADD_UINT(ctx, child, OID_AUTO, "ast_tx_intr", CTLFLAG_RD,
 	    &sc->sc_stats.ast_tx_intr, 0, "TX interrupts");
-
+	SYSCTL_ADD_UINT(ctx, child, OID_AUTO, "ast_tx_mcastq_overflow",
+	    CTLFLAG_RD, &sc->sc_stats.ast_tx_mcastq_overflow, 0,
+	    "Number of multicast frames exceeding maximum mcast queue depth");
+	
 	/* Attach the RX phy error array */
 	ath_sysctl_stats_attach_rxphyerr(sc, child);
 }
diff --git a/sys/dev/ath/if_ath_tx.c b/sys/dev/ath/if_ath_tx.c
index 93140347056..53c93204979 100644
--- a/sys/dev/ath/if_ath_tx.c
+++ b/sys/dev/ath/if_ath_tx.c
@@ -1369,7 +1369,7 @@ ath_tx_start(struct ath_softc *sc, struct ieee80211_node *ni,
 {
 	struct ieee80211vap *vap = ni->ni_vap;
 	struct ath_vap *avp = ATH_VAP(vap);
-	int r;
+	int r = 0;
 	u_int pri;
 	int tid;
 	struct ath_txq *txq;
@@ -1402,6 +1402,30 @@ ath_tx_start(struct ath_softc *sc, struct ieee80211_node *ni,
 	type = wh->i_fc[0] & IEEE80211_FC0_TYPE_MASK;
 	subtype = wh->i_fc[0] & IEEE80211_FC0_SUBTYPE_MASK;
 
+	/*
+	 * Enforce how deep the multicast queue can grow.
+	 *
+	 * XXX duplicated in ath_raw_xmit().
+	 */
+	if (IEEE80211_IS_MULTICAST(wh->i_addr1)) {
+		ATH_TXQ_LOCK(sc->sc_cabq);
+		ATH_TXQ_LOCK(&avp->av_mcastq);
+
+		if ((sc->sc_cabq->axq_depth + avp->av_mcastq.axq_depth) >
+		    sc->sc_txq_mcastq_maxdepth) {
+			sc->sc_stats.ast_tx_mcastq_overflow++;
+			r = ENOBUFS;
+		}
+
+		ATH_TXQ_UNLOCK(&avp->av_mcastq);
+		ATH_TXQ_UNLOCK(sc->sc_cabq);
+
+		if (r != 0) {
+			m_freem(m0);
+			return r;
+		}
+	}
+
 	/* A-MPDU TX */
 	is_ampdu_tx = ath_tx_ampdu_running(sc, ATH_NODE(ni), tid);
 	is_ampdu_pending = ath_tx_ampdu_pending(sc, ATH_NODE(ni), tid);
@@ -1734,7 +1758,10 @@ ath_raw_xmit(struct ieee80211_node *ni, struct mbuf *m,
 	struct ifnet *ifp = ic->ic_ifp;
 	struct ath_softc *sc = ifp->if_softc;
 	struct ath_buf *bf;
-	int error;
+	struct ieee80211_frame *wh = mtod(m, struct ieee80211_frame *);
+	struct ieee80211vap *vap = ni->ni_vap;
+	struct ath_vap *avp = ATH_VAP(vap);
+	int error = 0;
 
 	ATH_PCU_LOCK(sc);
 	if (sc->sc_inreset_cnt > 0) {
@@ -1755,6 +1782,31 @@ ath_raw_xmit(struct ieee80211_node *ni, struct mbuf *m,
 		error = ENETDOWN;
 		goto bad;
 	}
+
+	/*
+	 * Enforce how deep the multicast queue can grow.
+	 *
+	 * XXX duplicated in ath_tx_start().
+	 */
+	if (IEEE80211_IS_MULTICAST(wh->i_addr1)) {
+		ATH_TXQ_LOCK(sc->sc_cabq);
+		ATH_TXQ_LOCK(&avp->av_mcastq);
+
+		if ((sc->sc_cabq->axq_depth + avp->av_mcastq.axq_depth) >
+		    sc->sc_txq_mcastq_maxdepth) {
+			sc->sc_stats.ast_tx_mcastq_overflow++;
+			error = ENOBUFS;
+		}
+
+		ATH_TXQ_UNLOCK(&avp->av_mcastq);
+		ATH_TXQ_UNLOCK(sc->sc_cabq);
+
+		if (error != 0) {
+			m_freem(m);
+			goto bad;
+		}
+	}
+
 	/*
 	 * Grab a TX buffer and associated resources.
 	 */
diff --git a/sys/dev/ath/if_athioctl.h b/sys/dev/ath/if_athioctl.h
index 9c1cc12c72e..2e19ee47cd6 100644
--- a/sys/dev/ath/if_athioctl.h
+++ b/sys/dev/ath/if_athioctl.h
@@ -155,7 +155,8 @@ struct ath_stats {
 	u_int32_t	ast_rx_intr;
 	u_int32_t	ast_tx_aggr_ok;		/* aggregate TX ok */
 	u_int32_t	ast_tx_aggr_fail;	/* aggregate TX failed */
-	u_int32_t	ast_pad[2];
+	u_int32_t	ast_tx_mcastq_overflow;	/* multicast queue overflow */
+	u_int32_t	ast_pad[1];
 };
 
 #define	SIOCGATHSTATS	_IOWR('i', 137, struct ifreq)
diff --git a/sys/dev/ath/if_athvar.h b/sys/dev/ath/if_athvar.h
index 1b6542b650d..426c520364a 100644
--- a/sys/dev/ath/if_athvar.h
+++ b/sys/dev/ath/if_athvar.h
@@ -530,6 +530,31 @@ struct ath_softc {
 	int			sc_txchainmask;	/* currently configured TX chainmask */
 	int			sc_rxchainmask;	/* currently configured RX chainmask */
 
+	/* Queue limits */
+
+	/*
+	 * To avoid queue starvation in congested conditions,
+	 * these parameters tune the maximum number of frames
+	 * queued to the data/mcastq before they're dropped.
+	 *
+	 * This is to prevent:
+	 * + a single destination overwhelming everything, including
+	 *   management/multicast frames;
+	 * + multicast frames overwhelming everything (when the
+	 *   air is sufficiently busy that cabq can't drain.)
+	 *
+	 * These implement:
+	 * + data_minfree is the maximum number of free buffers
+	 *   overall to successfully allow a data frame.
+	 *
+	 * + mcastq_maxdepth is the maximum depth allowe dof the avp+cabq
+	 *   queue.  The avp is included in each comparison just to be
+	 *   a little overly conservative and this may end up being
+	 *   unhelpful with multiple VAPs.
+	 */
+	int			sc_txq_data_minfree;
+	int			sc_txq_mcastq_maxdepth;
+
 	/*
 	 * Aggregation twiddles
 	 *