--- Net2/netinet/in_systm.h	2018/04/24 18:03:54	1.1
+++ Net2/netinet/in_systm.h	2018/04/24 18:13:36	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)in_systm.h	7.4 (Berkeley) 6/28/90
+ *	from: @(#)in_systm.h	7.4 (Berkeley) 6/28/90
+ *	in_systm.h,v 1.3 1993/05/20 03:50:11 cgd Exp
  */
 
+#ifndef _NETINET_IN_SYSTM_H_
+#define _NETINET_IN_SYSTM_H_
+
 /*
  * Miscellaneous internetwork
  * definitions for kernel.
@@ -54,3 +58,5 @@ typedef	u_long	n_time;			/* ms since 00:
 #ifdef KERNEL
 n_time	iptime();
 #endif
+
+#endif /* !_NETINET_IN_SYSTM_H_ */