diff --git a/sys/dev/ath/ath_hal/ah.c b/sys/dev/ath/ath_hal/ah.c
index 7fff88b836b7..2d723bdae8d6 100644
--- a/sys/dev/ath/ath_hal/ah.c
+++ b/sys/dev/ath/ath_hal/ah.c
@@ -284,7 +284,8 @@ ath_hal_reverseBits(uint32_t val, uint32_t n)
  */
 uint32_t
 ath_hal_pkt_txtime(struct ath_hal *ah, const HAL_RATE_TABLE *rates, uint32_t frameLen,
-    uint16_t rateix, HAL_BOOL isht40, HAL_BOOL shortPreamble)
+    uint16_t rateix, HAL_BOOL isht40, HAL_BOOL shortPreamble,
+    HAL_BOOL includeSifs)
 {
 	uint8_t rc;
 	int numStreams;
@@ -293,7 +294,8 @@ ath_hal_pkt_txtime(struct ath_hal *ah, const HAL_RATE_TABLE *rates, uint32_t fra
 
 	/* Legacy rate? Return the old way */
 	if (! IS_HT_RATE(rc))
-		return ath_hal_computetxtime(ah, rates, frameLen, rateix, shortPreamble);
+		return ath_hal_computetxtime(ah, rates, frameLen, rateix,
+		    shortPreamble, includeSifs);
 
 	/* 11n frame - extract out the number of spatial streams */
 	numStreams = HT_RC_2_STREAMS(rc);
@@ -301,7 +303,9 @@ ath_hal_pkt_txtime(struct ath_hal *ah, const HAL_RATE_TABLE *rates, uint32_t fra
 	    ("number of spatial streams needs to be 1..3: MCS rate 0x%x!",
 	    rateix));
 
-	return ath_computedur_ht(frameLen, rc, numStreams, isht40, shortPreamble);
+	/* XXX TODO: Add SIFS */
+	return ath_computedur_ht(frameLen, rc, numStreams, isht40,
+	    shortPreamble);
 }
 
 static const uint16_t ht20_bps[32] = {
@@ -350,7 +354,7 @@ ath_computedur_ht(uint32_t frameLen, uint16_t rate, int streams,
 uint16_t
 ath_hal_computetxtime(struct ath_hal *ah,
 	const HAL_RATE_TABLE *rates, uint32_t frameLen, uint16_t rateix,
-	HAL_BOOL shortPreamble)
+	HAL_BOOL shortPreamble, HAL_BOOL includeSifs)
 {
 	uint32_t bitsPerSymbol, numBits, numSymbols, phyTime, txTime;
 	uint32_t kbps;
@@ -373,8 +377,10 @@ ath_hal_computetxtime(struct ath_hal *ah,
 		if (shortPreamble && rates->info[rateix].shortPreamble)
 			phyTime >>= 1;
 		numBits		= frameLen << 3;
-		txTime		= CCK_SIFS_TIME + phyTime
+		txTime		= phyTime
 				+ ((numBits * 1000)/kbps);
+		if (includeSifs)
+			txTime	+= CCK_SIFS_TIME;
 		break;
 	case IEEE80211_T_OFDM:
 		bitsPerSymbol	= (kbps * OFDM_SYMBOL_TIME) / 1000;
@@ -382,9 +388,10 @@ ath_hal_computetxtime(struct ath_hal *ah,
 
 		numBits		= OFDM_PLCP_BITS + (frameLen << 3);
 		numSymbols	= howmany(numBits, bitsPerSymbol);
-		txTime		= OFDM_SIFS_TIME
-				+ OFDM_PREAMBLE_TIME
+		txTime		= OFDM_PREAMBLE_TIME
 				+ (numSymbols * OFDM_SYMBOL_TIME);
+		if (includeSifs)
+			txTime	+= OFDM_SIFS_TIME;
 		break;
 	case IEEE80211_T_OFDM_HALF:
 		bitsPerSymbol	= (kbps * OFDM_HALF_SYMBOL_TIME) / 1000;
@@ -392,9 +399,10 @@ ath_hal_computetxtime(struct ath_hal *ah,
 
 		numBits		= OFDM_HALF_PLCP_BITS + (frameLen << 3);
 		numSymbols	= howmany(numBits, bitsPerSymbol);
-		txTime		= OFDM_HALF_SIFS_TIME
-				+ OFDM_HALF_PREAMBLE_TIME
+		txTime		= OFDM_HALF_PREAMBLE_TIME
 				+ (numSymbols * OFDM_HALF_SYMBOL_TIME);
+		if (includeSifs)
+			txTime	+= OFDM_HALF_SIFS_TIME;
 		break;
 	case IEEE80211_T_OFDM_QUARTER:
 		bitsPerSymbol	= (kbps * OFDM_QUARTER_SYMBOL_TIME) / 1000;
@@ -402,9 +410,10 @@ ath_hal_computetxtime(struct ath_hal *ah,
 
 		numBits		= OFDM_QUARTER_PLCP_BITS + (frameLen << 3);
 		numSymbols	= howmany(numBits, bitsPerSymbol);
-		txTime		= OFDM_QUARTER_SIFS_TIME
-				+ OFDM_QUARTER_PREAMBLE_TIME
+		txTime		= OFDM_QUARTER_PREAMBLE_TIME
 				+ (numSymbols * OFDM_QUARTER_SYMBOL_TIME);
+		if (includeSifs)
+			txTime	+= OFDM_QUARTER_SIFS_TIME;
 		break;
 	case IEEE80211_T_TURBO:
 		bitsPerSymbol	= (kbps * TURBO_SYMBOL_TIME) / 1000;
@@ -412,9 +421,10 @@ ath_hal_computetxtime(struct ath_hal *ah,
 
 		numBits		= TURBO_PLCP_BITS + (frameLen << 3);
 		numSymbols	= howmany(numBits, bitsPerSymbol);
-		txTime		= TURBO_SIFS_TIME
-				+ TURBO_PREAMBLE_TIME
+		txTime		= TURBO_PREAMBLE_TIME
 				+ (numSymbols * TURBO_SYMBOL_TIME);
+		if (includeSifs)
+			txTime	+= TURBO_SIFS_TIME;
 		break;
 	default:
 		HALDEBUG(ah, HAL_DEBUG_PHYIO,
@@ -588,9 +598,9 @@ ath_hal_setupratetable(struct ath_hal *ah, HAL_RATE_TABLE *rt)
 		 *     2Mb/s rate which will work but is suboptimal
 		 */
 		rt->info[i].lpAckDuration = ath_hal_computetxtime(ah, rt,
-			WLAN_CTRL_FRAME_SIZE, cix, AH_FALSE);
+			WLAN_CTRL_FRAME_SIZE, cix, AH_FALSE, AH_TRUE);
 		rt->info[i].spAckDuration = ath_hal_computetxtime(ah, rt,
-			WLAN_CTRL_FRAME_SIZE, cix, AH_TRUE);
+			WLAN_CTRL_FRAME_SIZE, cix, AH_TRUE, AH_TRUE);
 	}
 #undef N
 }
diff --git a/sys/dev/ath/ath_hal/ah.h b/sys/dev/ath/ath_hal/ah.h
index ab907658f1ed..519fcb8338df 100644
--- a/sys/dev/ath/ath_hal/ah.h
+++ b/sys/dev/ath/ath_hal/ah.h
@@ -1626,7 +1626,8 @@ extern	int ath_hal_get_curmode(struct ath_hal *ah,
  */
 extern uint32_t __ahdecl ath_hal_pkt_txtime(struct ath_hal *ah,
     const HAL_RATE_TABLE *rates, uint32_t frameLen,
-    uint16_t rateix, HAL_BOOL isht40, HAL_BOOL shortPreamble);
+    uint16_t rateix, HAL_BOOL isht40, HAL_BOOL shortPreamble,
+    HAL_BOOL includeSifs);
 
 /*
  * Calculate the duration of an 11n frame.
@@ -1639,7 +1640,8 @@ extern uint32_t __ahdecl ath_computedur_ht(uint32_t frameLen, uint16_t rate,
  */
 extern uint16_t __ahdecl ath_hal_computetxtime(struct ath_hal *,
 		const HAL_RATE_TABLE *rates, uint32_t frameLen,
-		uint16_t rateix, HAL_BOOL shortPreamble);
+		uint16_t rateix, HAL_BOOL shortPreamble,
+		HAL_BOOL includeSifs);
 
 /*
  * Adjust the TSF.
diff --git a/sys/dev/ath/ath_hal/ar5212/ar5212_reset.c b/sys/dev/ath/ath_hal/ar5212/ar5212_reset.c
index 6a76f4329fb2..7c9158e91d2b 100644
--- a/sys/dev/ath/ath_hal/ar5212/ar5212_reset.c
+++ b/sys/dev/ath/ath_hal/ar5212/ar5212_reset.c
@@ -2735,7 +2735,7 @@ ar5212SetRateDurationTable(struct ath_hal *ah,
 			AR_RATE_DURATION(rt->info[i].rateCode),
 			ath_hal_computetxtime(ah, rt,
 				WLAN_CTRL_FRAME_SIZE,
-				rt->info[i].controlRate, AH_FALSE));
+				rt->info[i].controlRate, AH_FALSE, AH_TRUE));
 	if (!IEEE80211_IS_CHAN_TURBO(chan)) {
 		/* 11g Table is used to cover the CCK rates. */
 		rt = ar5212GetRateTable(ah, HAL_MODE_11G);
@@ -2748,7 +2748,8 @@ ar5212SetRateDurationTable(struct ath_hal *ah,
 			OS_REG_WRITE(ah, reg,
 				ath_hal_computetxtime(ah, rt,
 					WLAN_CTRL_FRAME_SIZE,
-					rt->info[i].controlRate, AH_FALSE));
+					rt->info[i].controlRate, AH_FALSE,
+					AH_TRUE));
 			/* cck rates have short preamble option also */
 			if (rt->info[i].shortPreamble) {
 				reg += rt->info[i].shortPreamble << 2;
@@ -2756,7 +2757,7 @@ ar5212SetRateDurationTable(struct ath_hal *ah,
 					ath_hal_computetxtime(ah, rt,
 						WLAN_CTRL_FRAME_SIZE,
 						rt->info[i].controlRate,
-						AH_TRUE));
+						AH_TRUE, AH_TRUE));
 			}
 		}
 	}
diff --git a/sys/dev/ath/ath_rate/sample/sample.h b/sys/dev/ath/ath_rate/sample/sample.h
index 5495141c60be..82037d7e935d 100644
--- a/sys/dev/ath/ath_rate/sample/sample.h
+++ b/sys/dev/ath/ath_rate/sample/sample.h
@@ -212,9 +212,9 @@ static unsigned calc_usecs_unicast_packet(struct ath_softc *sc,
 		if (rts)		/* SIFS + CTS */
 			ctsduration += rt->info[cix].spAckDuration;
 
-		/* XXX assumes short preamble */
+		/* XXX assumes short preamble, include SIFS */
 		ctsduration += ath_hal_pkt_txtime(sc->sc_ah, rt, length, rix,
-		    is_ht40, 0);
+		    is_ht40, 0, 1);
 
 		if (cts)	/* SIFS + ACK */
 			ctsduration += rt->info[cix].spAckDuration;
@@ -223,9 +223,9 @@ static unsigned calc_usecs_unicast_packet(struct ath_softc *sc,
 	}
 	tt += t_difs;
 
-	/* XXX assumes short preamble */
+	/* XXX assumes short preamble, include SIFS */
 	tt += (long_retries+1)*ath_hal_pkt_txtime(sc->sc_ah, rt, length, rix,
-	    is_ht40, 0);
+	    is_ht40, 0, 1);
 
 	tt += (long_retries+1)*(t_sifs + rt->info[rix].spAckDuration);
 
diff --git a/sys/dev/ath/if_ath_beacon.c b/sys/dev/ath/if_ath_beacon.c
index c700230149e5..1d1aa26831ce 100644
--- a/sys/dev/ath/if_ath_beacon.c
+++ b/sys/dev/ath/if_ath_beacon.c
@@ -347,7 +347,7 @@ ath_beacon_setup(struct ath_softc *sc, struct ath_buf *bf)
 		rc[0].tx_power_cap = 0x3f;
 		rc[0].PktDuration =
 		    ath_hal_computetxtime(ah, rt, roundup(m->m_len, 4),
-		        rix, 0);
+		        rix, 0, AH_TRUE);
 		ath_hal_set11nratescenario(ah, ds, 0, 0, rc, 4, flags);
 	}
 
diff --git a/sys/dev/ath/if_ath_tdma.c b/sys/dev/ath/if_ath_tdma.c
index e3460c6374c3..c29da1b1de89 100644
--- a/sys/dev/ath/if_ath_tdma.c
+++ b/sys/dev/ath/if_ath_tdma.c
@@ -288,7 +288,8 @@ ath_tdma_config(struct ath_softc *sc, struct ieee80211vap *vap)
 		/* XXX short preamble assumed */
 		/* XXX non-11n rate assumed */
 		sc->sc_tdmaguard = ath_hal_computetxtime(ah, sc->sc_currates,
-		    vap->iv_ifp->if_mtu + IEEE80211_MAXOVERHEAD, rix, AH_TRUE);
+		    vap->iv_ifp->if_mtu + IEEE80211_MAXOVERHEAD, rix, AH_TRUE,
+		    AH_TRUE);
 	}
 
 	ath_hal_intrset(ah, 0);
@@ -430,7 +431,8 @@ ath_tdma_update(struct ieee80211_node *ni,
 	    rix,
 	    !! (rs->rs_flags & HAL_RX_2040),
 	    (rix & 0x80) ?
-	      (! (rs->rs_flags & HAL_RX_GI)) : rt->info[rix].shortPreamble);
+	      (! (rs->rs_flags & HAL_RX_GI)) : rt->info[rix].shortPreamble,
+	    AH_TRUE);
 	/* NB: << 9 is to cvt to TU and /2 */
 	nextslot = (rstamp - txtime) + (sc->sc_tdmabintval << 9);
 
diff --git a/sys/dev/ath/if_ath_tx.c b/sys/dev/ath/if_ath_tx.c
index d2b1d85ea9e3..fadfed3cc61f 100644
--- a/sys/dev/ath/if_ath_tx.c
+++ b/sys/dev/ath/if_ath_tx.c
@@ -1131,7 +1131,8 @@ ath_tx_calc_duration(struct ath_softc *sc, struct ath_buf *bf)
 			dur += ath_hal_computetxtime(ah,
 			    rt,
 			    bf->bf_nextfraglen,
-			    rix, shortPreamble);
+			    rix, shortPreamble,
+			    AH_TRUE);
 		}
 		if (isfrag) {
 			/*
@@ -1201,14 +1202,14 @@ ath_tx_calc_ctsduration(struct ath_hal *ah, int rix, int cix,
 		if (flags & HAL_TXDESC_RTSENA)		/* SIFS + CTS */
 			ctsduration += rt->info[cix].spAckDuration;
 		ctsduration += ath_hal_computetxtime(ah,
-			rt, pktlen, rix, AH_TRUE);
+			rt, pktlen, rix, AH_TRUE, AH_TRUE);
 		if ((flags & HAL_TXDESC_NOACK) == 0)	/* SIFS + ACK */
 			ctsduration += rt->info[rix].spAckDuration;
 	} else {
 		if (flags & HAL_TXDESC_RTSENA)		/* SIFS + CTS */
 			ctsduration += rt->info[cix].lpAckDuration;
 		ctsduration += ath_hal_computetxtime(ah,
-			rt, pktlen, rix, AH_FALSE);
+			rt, pktlen, rix, AH_FALSE, AH_TRUE);
 		if ((flags & HAL_TXDESC_NOACK) == 0)	/* SIFS + ACK */
 			ctsduration += rt->info[rix].lpAckDuration;
 	}
diff --git a/sys/dev/ath/if_ath_tx_ht.c b/sys/dev/ath/if_ath_tx_ht.c
index 5a55f60762df..c4d71301da98 100644
--- a/sys/dev/ath/if_ath_tx_ht.c
+++ b/sys/dev/ath/if_ath_tx_ht.c
@@ -296,8 +296,6 @@ ath_tx_rate_fill_rcflags(struct ath_softc *sc, struct ath_buf *bf)
 			 * can receive (at least) 1 stream STBC, AND it's
 			 * MCS 0-7, AND we have at least two chains enabled,
 			 * enable STBC.
-			 *
-			 * XXX TODO: .. and the rate is an 11n rate?
 			 */
 			if (ic->ic_htcaps & IEEE80211_HTCAP_TXSTBC &&
 			    ni->ni_vap->iv_flags_ht & IEEE80211_FHT_STBC_TX &&
@@ -621,8 +619,9 @@ ath_rateseries_setup(struct ath_softc *sc, struct ieee80211_node *ni,
 			if (shortPreamble)
 				series[i].Rate |=
 				    rt->info[rc[i].rix].shortPreamble;
+			/* XXX TODO: don't include SIFS */
 			series[i].PktDuration = ath_hal_computetxtime(ah,
-			    rt, pktlen, rc[i].rix, shortPreamble);
+			    rt, pktlen, rc[i].rix, shortPreamble, AH_TRUE);
 		}
 	}
 }