--- a/urngd.c
+++ b/urngd.c
@@ -114,7 +114,7 @@ static size_t gather_entropy(struct urng
 
 	ret = write_entropy(u, buf, sizeof(buf), ENTROPYBYTES);
 	if (sizeof(buf) != ret) {
-		ERROR("injected %lub of entropy, less then %db expected\n",
+		ERROR("injected %zub of entropy, less then %db expected\n",
 		      ret, sizeof(buf));
 	} else {
 		ret = sizeof(buf);