--- Net2/sys/mbuf.h	2018/04/24 18:03:57	1.1.1.1
+++ Net2/sys/mbuf.h	2018/04/24 18:16:02	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)mbuf.h	7.14 (Berkeley) 12/5/90
+ *	from: @(#)mbuf.h	7.14 (Berkeley) 12/5/90
+ *	mbuf.h,v 1.3 1993/05/20 16:22:39 cgd Exp
  */
 
+#ifndef _SYS_MBUF_H_
+#define _SYS_MBUF_H_
+
 #ifndef M_WAITOK
 #include "malloc.h"
 #endif
@@ -380,3 +384,5 @@ int mbtypes[] = {				/* XXX */
 };
 #endif
 #endif
+
+#endif /* !_SYS_MBUF_H_ */