diff --git a/lib/isc/unix/socket.c b/lib/isc/unix/socket.c
index a04e2d1f2a..fd767100bd 100644
--- a/lib/isc/unix/socket.c
+++ b/lib/isc/unix/socket.c
@@ -1857,7 +1857,7 @@ dump_msg(struct msghdr *msg) {
 	printf("\tiov %p, iovlen %ld\n", msg->msg_iov,
 	       (long) msg->msg_iovlen);
 	for (i = 0; i < (unsigned int)msg->msg_iovlen; i++)
-		printf("\t\t%d\tbase %p, len %ld\n", i,
+		printf("\t\t%u\tbase %p, len %ld\n", i,
 		       msg->msg_iov[i].iov_base,
 		       (long) msg->msg_iov[i].iov_len);
 #ifdef ISC_NET_BSD44MSGHDR