diff -r 0a8671f32424 -r 7132acfd287e plugins/mod_s2s.lua
--- a/plugins/mod_s2s.lua	Sun Jul 18 09:08:04 2021 +0200
+++ b/plugins/mod_s2s.lua	Sun Jul 18 09:17:31 2021 +0200
@@ -645,7 +645,7 @@
 			session.sends2s(stream_error);
 		end
 	else
-		m_closed_connections:with_labels(this_host, session.direction, reason == false and ":remote-choice" or ":local-choice"):add(1)
+		m_closed_connections:with_labels(this_host or ":unknown", session.direction, reason == false and ":remote-choice" or ":local-choice"):add(1)
 	end
 
 	session.sends2s("</stream:stream>");