--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -673,6 +673,7 @@ static enum ATH_AGGR_STATUS ath_tx_form_
 	u16 aggr_limit = 0, al = 0, bpad = 0,
 		al_delta, h_baw = tid->baw_size / 2;
 	enum ATH_AGGR_STATUS status = ATH_AGGR_DONE;
+	struct ieee80211_tx_info *tx_info;
 
 	bf_first = list_first_entry(&tid->buf_q, struct ath_buf, list);
 
@@ -699,6 +700,11 @@ static enum ATH_AGGR_STATUS ath_tx_form_
 			break;
 		}
 
+		tx_info = IEEE80211_SKB_CB(bf->bf_mpdu);
+		if (nframes && ((tx_info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) ||
+			!(tx_info->control.rates[0].flags & IEEE80211_TX_RC_MCS)))
+			break;
+
 		/* do not exceed subframe limit */
 		if (nframes >= min((int)h_baw, ATH_AMPDU_SUBFRAME_DEFAULT)) {
 			status = ATH_AGGR_LIMITED;