diff --git a/src/include/unistd.h b/src/include/unistd.h
index 02917118..3ffcec0f 100644
--- a/src/include/unistd.h
+++ b/src/include/unistd.h
@@ -143,6 +143,7 @@ int	 re_exec __P((const char *));
 int	 readlink __P((const char *, char *, int));
 int	 reboot __P((int));
 int	 revoke __P((const char *));
+int	 rfork __P((int opts));
 int	 rresvport __P((int *));
 int	 ruserok __P((const char *, int, const char *, const char *));
 char	*sbrk __P((int));