diff --git a/include/gsup_protocol.hrl b/include/gsup_protocol.hrl
index 3f04ece..e304654 100644
--- a/include/gsup_protocol.hrl
+++ b/include/gsup_protocol.hrl
@@ -167,7 +167,7 @@
 
 -define(MANDATORY_DEFAULT, [imsi, message_type]).
 
--define(OPTIONAL_DEFAULT, [message_class]).
+-define(OPTIONAL_DEFAULT, [message_class, source_name, destination_name]).
 
 -define (GSUP_MESSAGES(), #{
   16#04 => #{message_type => location_upd_req, mandatory => [], optional => [cn_domain]},