diff --git a/sys/netinet/tcp.h b/sys/netinet/tcp.h
--- a/sys/netinet/tcp.h
+++ b/sys/netinet/tcp.h
@@ -55,12 +55,12 @@
 	tcp_seq	th_seq;			/* sequence number */
 	tcp_seq	th_ack;			/* acknowledgement number */
 #if BYTE_ORDER == LITTLE_ENDIAN
-	u_char	th_x2:4,		/* (unused) */
+	u_char	th_x2:4,		/* upper 4 (reserved) flags */
 		th_off:4;		/* data offset */
 #endif
 #if BYTE_ORDER == BIG_ENDIAN
 	u_char	th_off:4,		/* data offset */
-		th_x2:4;		/* (unused) */
+		th_x2:4;		/* upper 4 (reserved) flags */
 #endif
 	u_char	th_flags;
 #define	TH_FIN	0x01
diff --git a/sys/netinet/tcp_lro.h b/sys/netinet/tcp_lro.h
--- a/sys/netinet/tcp_lro.h
+++ b/sys/netinet/tcp_lro.h
@@ -42,20 +42,20 @@
 
 /*
  * Flags for ACK entry for compression
- * the bottom 8 bits has the th_flags.
+ * the bottom 12 bits has the th_x2|th_flags.
  * LRO itself adds only the TSTMP flags
  * to indicate if either of the types
  * of timestamps are filled and the
  * HAS_TSTMP option to indicate if the
  * TCP timestamp option is valid.
  *
- * The other 5 flag bits are for processing
+ * The other 1 flag bits are for processing
  * by a stack.
  *
  */
-#define TSTMP_LRO		0x0100
-#define TSTMP_HDWR		0x0200
-#define HAS_TSTMP		0x0400
+#define TSTMP_LRO		0x1000
+#define TSTMP_HDWR		0x2000
+#define HAS_TSTMP		0x4000
 /*
  * Default number of interrupts on the same cpu in a row
  * that will cause us to declare a "affinity cpu".
@@ -146,9 +146,10 @@
 	uint16_t		compressed;
 	uint16_t		uncompressed;
 	uint16_t		window;
-	uint8_t			flags;
-	uint8_t			timestamp : 1;
-	uint8_t			needs_merge : 1;
+	uint16_t		flags : 12,	/* 12 TCP header bits */
+				timestamp : 1,
+				needs_merge : 1,
+				reserved : 2;	/* unused */
 	struct bintime		alloc_time;	/* time when entry was allocated */
 };
 
diff --git a/sys/netinet/tcp_lro.c b/sys/netinet/tcp_lro.c
--- a/sys/netinet/tcp_lro.c
+++ b/sys/netinet/tcp_lro.c
@@ -921,7 +921,7 @@
 	le->next_seq = ntohl(th->th_seq) + tcp_data_len;
 	le->ack_seq = th->th_ack;
 	le->window = th->th_win;
-	le->flags = th->th_flags;
+	le->flags = (th->th_x2 << 8) | th->th_flags;
 	le->needs_merge = 0;
 
 	/* Setup new data pointers. */
@@ -1033,7 +1033,7 @@
 		tcp_push_and_replace(lc, le, m);
 		goto again;
 	}
-	if ((th->th_flags & ~(TH_ACK | TH_PUSH)) != 0) {
+	if ((((th->th_x2 << 8) | th->th_flags) & ~(TH_ACK | TH_PUSH)) != 0) {
 		/*
 		 * Make sure that previously seen segments/ACKs are delivered
 		 * before this segment, e.g. FIN.
@@ -1077,7 +1077,7 @@
 			tcp_push_and_replace(lc, le, m);
 			goto again;
 		}
-		if ((th->th_flags & ~(TH_ACK | TH_PUSH)) != 0) {
+		if ((((th->th_x2 << 8) | th->th_flags) & ~(TH_ACK | TH_PUSH)) != 0) {
 			tcp_push_and_replace(lc, le, m);
 			goto again;
 		}
@@ -1265,7 +1265,7 @@
 		break;
 	}
 	/* For ACKCMP we only accept ACK, PUSH, ECE and CWR. */
-	if ((th->th_flags & ~(TH_ACK | TH_PUSH | TH_ECE | TH_CWR)) != 0)
+	if ((((th->th_x2 << 8) | th->th_flags) & ~(TH_ACK | TH_PUSH | TH_ECE | TH_CWR)) != 0)
 		ret = false;
 	/* If it has data on it we cannot compress it */
 	if (m->m_pkthdr.lro_tcp_d_len)
@@ -1576,7 +1576,7 @@
 		ae->flags = TSTMP_HDWR;
 	ae->seq = ntohl(th->th_seq);
 	ae->ack = ntohl(th->th_ack);
-	ae->flags |= th->th_flags;
+	ae->flags |= (th->th_x2 << 8) | th->th_flags;
 	if (ts_ptr != NULL) {
 		ae->ts_value = ntohl(ts_ptr[1]);
 		ae->ts_echo = ntohl(ts_ptr[2]);