diff --git a/tools/kwbimage.c b/tools/kwbimage.c
index d200ff2..e72555f 100644
--- a/tools/kwbimage.c
+++ b/tools/kwbimage.c
@@ -542,7 +542,7 @@
 	}
 
 	if (4 + size_seq > sizeof(dst->key)) {
-		fprintf(stderr, "export pk failed: seq too large (%d, %lu)\n",
+		fprintf(stderr, "export pk failed: seq too large (%d, %zu)\n",
 			4 + size_seq, sizeof(dst->key));
 		fprintf(stderr, errmsg, keyname);
 		return -ENOBUFS;