diff --git a/tcp.c b/tcp.c
index e91c0cf..697f80d 100644
--- a/tcp.c
+++ b/tcp.c
@@ -339,7 +339,7 @@ enum {
 #define MSS_DEFAULT			536
 #define WINDOW_DEFAULT			14600		/* RFC 6928 */
 
-#define ACK_INTERVAL			10		/* ms */
+#define ACK_INTERVAL			1		/* ms */
 #define SYN_TIMEOUT			10		/* s */
 #define ACK_TIMEOUT			2
 #define FIN_TIMEOUT			60
@@ -1097,9 +1097,22 @@ int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
 	if ((conn->flags & LOCAL) || tcp_rtt_dst_low(conn)) {
 		new_wnd_to_tap = tinfo->tcpi_snd_wnd;
 	} else {
+		uint32_t sendq;
+		int limit;
+
+		ioctl(s, SIOCOUTQ, &sendq);
 		tcp_get_sndbuf(conn);
+
+		if ((int)sendq > SNDBUF_GET(conn))
+			limit = 0;
+		else
+			limit = SNDBUF_GET(conn) - (int)sendq;
+
+		if (limit < MSS_GET(conn))
+			limit = 0;
+
 		new_wnd_to_tap = MIN((int)tinfo->tcpi_snd_wnd,
-				     SNDBUF_GET(conn));
+				     limit);
 	}
 
 	new_wnd_to_tap = MIN(new_wnd_to_tap, MAX_WINDOW);
@@ -1240,7 +1253,8 @@ int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn,
 	th->fin = !!(flags & FIN);
 
 	if (th->ack) {
-		if (SEQ_GE(conn->seq_ack_to_tap, conn->seq_from_tap))
+		if (SEQ_GE(conn->seq_ack_to_tap, conn->seq_from_tap) &&
+		    conn->wnd_to_tap > MSS_GET(conn))
 			conn_flag(c, conn, ~ACK_TO_TAP_DUE);
 		else
 			conn_flag(c, conn, ACK_TO_TAP_DUE);