diff --git a/sys/sys/unistd.h b/sys/sys/unistd.h
index 450d841f4bd..28acd7da4e8 100644
--- a/sys/sys/unistd.h
+++ b/sys/sys/unistd.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)unistd.h	8.2 (Berkeley) 1/7/94
- * $Id: unistd.h,v 1.6 1996/04/17 17:05:08 smpatel Exp $
+ * $Id: unistd.h,v 1.7 1996/08/20 07:23:35 smpatel Exp $
  */
 
 #ifndef _SYS_UNISTD_H_
@@ -119,6 +119,7 @@
 /* configurable system strings */
 #define	_CS_PATH		 1
 
+#ifndef _POSIX_SOURCE
 /*
  * rfork() options.
  *
@@ -135,6 +136,6 @@
 #define RFCENVG		(1<<11) /* UNIMPL zero plan9 `env space' */
 #define RFCFDG		(1<<12) /* zero fd table */
 #define RFPPWAIT	(1<<31) /* parent sleeps until child exits (vfork) */
-
+#endif /* !_POSIX_SOURCE */
 
 #endif /* !_SYS_UNISTD_H_ */