diff --git a/tests/server/mqttd.c b/tests/server/mqttd.c
index 7b5c7c8043..23eefa65aa 100644
--- a/tests/server/mqttd.c
+++ b/tests/server/mqttd.c
@@ -155,7 +155,7 @@ static void logprotocol(mqttdir dir,
   }
   fprintf(output, "%s %s %x %s\n",
           dir == FROM_CLIENT ? "client" : "server",
-          prefix, (int)remlen, data);
+          prefix, (unsigned int)remlen, data);
 }
 
 /* return 0 on success */