diff --git a/usr.bin/systat/extern.h b/usr.bin/systat/extern.h
index b3a01290522..81b660a7d0d 100644
--- a/usr.bin/systat/extern.h
+++ b/usr.bin/systat/extern.h
@@ -90,7 +90,7 @@ void	 die __P((int));
 void	 display __P((int));
 int	 dkinit __P((void));
 int	 dkcmd __P((char *, char *));
-void	 error __P((const char *fmt, ...));
+void	 error __P((const char *fmt, ...)) __printflike(1, 2);
 void	 fetchicmp __P((void));
 void	 fetchip __P((void));
 void	 fetchiostat __P((void));
diff --git a/usr.bin/systat/swap.c b/usr.bin/systat/swap.c
index f4b3267ed50..18aa0324ecb 100644
--- a/usr.bin/systat/swap.c
+++ b/usr.bin/systat/swap.c
@@ -101,7 +101,7 @@ initswap()
 
 	if (kvm_getswapinfo(kd, &dummy, 1, 0) < 0) {
 		snprintf(msgbuf, sizeof(msgbuf), "systat: kvm_getswapinfo failed");
-		error(msgbuf);
+		error("%s", msgbuf);
 		return (0);
 	}