diff --git a/stand/libsa/arp.c b/stand/libsa/arp.c
index 7d49559b4e0..9152cb2773d 100644
--- a/stand/libsa/arp.c
+++ b/stand/libsa/arp.c
@@ -178,7 +178,7 @@ arprecv(struct iodesc *d, void **pkt, void **payload, time_t tleft, void *extra)
 	if (n == -1 || n < sizeof(struct ether_arp)) {
 #ifdef ARP_DEBUG
 		if (debug)
-			printf("bad len=%d\n", n);
+			printf("bad len=%zd\n", n);
 #endif
 		free(ptr);
 		return (-1);