diff --git a/usr.bin/mktemp/mktemp.c b/usr.bin/mktemp/mktemp.c
index b58ac4b9d055..72b89d607889 100644
--- a/usr.bin/mktemp/mktemp.c
+++ b/usr.bin/mktemp/mktemp.c
@@ -143,7 +143,7 @@ main(int argc, char **argv)
 }
 
 static void
-usage()
+usage(void)
 {
 	fprintf(stderr,
 		"usage: mktemp [-d] [-q] [-t prefix] [-u] template ...\n");