diff --git a/slirp/mbuf.h b/slirp/mbuf.h
index 55170e517bd2e6c11b97e4133370df09169815af..0708840f04e78d675b623043ae980e697e7e32d9 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -82,12 +82,13 @@ struct m_hdr {
 struct mbuf {
 	struct	m_hdr m_hdr;
 	Slirp *slirp;
+	bool	arp_requested;
+	uint64_t expiration_date;
+	/* start of dynamic buffer area, must be last element */
 	union M_dat {
 		char	m_dat_[1]; /* ANSI don't like 0 sized arrays */
 		char	*m_ext_;
 	} M_dat;
-    bool     arp_requested;
-    uint64_t expiration_date;
 };
 
 #define m_next		m_hdr.mh_next
diff --git a/slirp/tcp_input.c b/slirp/tcp_input.c
index 2f1a196b391d8f5a0f287088cd55c227b78b9414..942aaf44f1b9e11965c3020d014cf40327bbe5d7 100644
--- a/slirp/tcp_input.c
+++ b/slirp/tcp_input.c
@@ -1156,6 +1156,16 @@ step6:
 			tp->rcv_up = tp->rcv_nxt;
 dodata:
 
+	/*
+	 * If this is a small packet, then ACK now - with Nagel
+	 *      congestion avoidance sender won't send more until
+	 *      he gets an ACK.
+	 */
+	if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
+	    ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
+		tp->t_flags |= TF_ACKNOW;
+	}
+
 	/*
 	 * Process the segment text, merging it into the TCP sequencing queue,
 	 * and arranging for acknowledgment of receipt if necessary.
@@ -1234,18 +1244,6 @@ dodata:
 		}
 	}
 
-	/*
-	 * If this is a small packet, then ACK now - with Nagel
-	 *      congestion avoidance sender won't send more until
-	 *      he gets an ACK.
-	 *
-	 * See above.
-	 */
-	if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
-	    ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
-		tp->t_flags |= TF_ACKNOW;
-	}
-
 	/*
 	 * Return any desired output.
 	 */