diff --git a/newlib/libc/sys/rtems/include/netinet/tcp.h b/newlib/libc/sys/rtems/include/netinet/tcp.h
index 6dc7403aa..6a3603287 100644
--- a/newlib/libc/sys/rtems/include/netinet/tcp.h
+++ b/newlib/libc/sys/rtems/include/netinet/tcp.h
@@ -55,12 +55,12 @@ struct tcphdr {
 	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