diff --git a/src/sink.c b/src/sink.c
index 9eca4814b..ff498b24d 100644
--- a/src/sink.c
+++ b/src/sink.c
@@ -993,7 +993,7 @@ int cfg_post_parse_ring()
 	if (cfg_sink && (cfg_sink->type == SINK_TYPE_BUFFER)) {
 		if (cfg_sink->maxlen > b_size(&cfg_sink->ctx.ring->buf)) {
 			ha_warning("ring '%s' event max length '%u' exceeds size, forced to size '%lu'.\n",
-			           cfg_sink->name, cfg_sink->maxlen, b_size(&cfg_sink->ctx.ring->buf));
+			           cfg_sink->name, cfg_sink->maxlen, (unsigned long)b_size(&cfg_sink->ctx.ring->buf));
 			cfg_sink->maxlen = b_size(&cfg_sink->ctx.ring->buf);
 			err_code |= ERR_ALERT;
 		}