diff --git a/usr.sbin/ac/Makefile b/usr.sbin/ac/Makefile
index 0fac2fbdbab9..5ddc6e41081e 100644
--- a/usr.sbin/ac/Makefile
+++ b/usr.sbin/ac/Makefile
@@ -1,6 +1,7 @@
 # $FreeBSD$
 
 PROG=	ac
+WARNS?=	2
 MAN=	ac.8
 
 # If "CONSOLE_TTY" is not defined, this program is compatible with the
diff --git a/usr.sbin/ac/ac.c b/usr.sbin/ac/ac.c
index e6b0ae2e18d3..3b2c39db68ba 100644
--- a/usr.sbin/ac/ac.c
+++ b/usr.sbin/ac/ac.c
@@ -87,11 +87,11 @@ int			main __P((int, char **));
 int			ac __P((FILE *));
 struct tty_list		*add_tty __P((char *));
 int			do_tty __P((char *));
-FILE			*file __P((char *));
+FILE			*file __P((const char *));
 struct utmp_list	*log_in __P((struct utmp_list *, struct utmp *));
 struct utmp_list	*log_out __P((struct utmp_list *, struct utmp *));
 int			on_console __P((struct utmp_list *));
-void			show __P((char *, time_t));
+void			show __P((const char *, time_t));
 void			show_today __P((struct user_list *, struct utmp_list *,
 			    time_t));
 void			show_users __P((struct user_list *));
@@ -103,7 +103,7 @@ void			usage __P((void));
  */
 FILE *
 file(name)
-	char *name;
+	const char *name;
 {
 	FILE *fp;
 
@@ -293,7 +293,7 @@ main(argc, argv)
  */
 void
 show(name, secs)
-	char *name;
+	const char *name;
 	time_t secs;
 {
 	(void)printf("\t%-*s %8.2f\n", UT_NAMESIZE, name,