--- Net2/sys/domain.h	2018/04/24 18:03:58	1.1.1.1
+++ Net2/sys/domain.h	2018/04/24 18:16:55	1.1.1.2
@@ -30,9 +30,13 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	@(#)domain.h	7.4 (Berkeley) 6/28/90
+ *	from: @(#)domain.h	7.4 (Berkeley) 6/28/90
+ *	domain.h,v 1.3 1993/05/20 16:22:08 cgd Exp
  */
 
+#ifndef _SYS_DOMAIN_H_
+#define _SYS_DOMAIN_H_
+
 /*
  * Structure per communications domain.
  */
@@ -49,3 +53,5 @@ struct	domain {
 #ifdef KERNEL
 struct	domain *domains;
 #endif
+
+#endif /* !_SYS_DOMAIN_H_ */