diff --git a/library/GSUP_Templates.ttcn b/library/GSUP_Templates.ttcn
index 9daf9c0..6d14b02 100644
--- a/library/GSUP_Templates.ttcn
+++ b/library/GSUP_Templates.ttcn
@@ -374,7 +374,7 @@
 	ts_GSUP(OSMO_GSUP_MSGT_SEND_AUTH_INFO_RESULT, {
 		valueof(ts_GSUP_IE_IMSI(imsi)), auth_tuple });
 
-template GSUP_PDU tr_GSUP_SAI_ERR(template hexstring imsi, template integer cause) :=
+template GSUP_PDU tr_GSUP_SAI_ERR(template hexstring imsi, template (present) integer cause := ?) :=
 	tr_GSUP(OSMO_GSUP_MSGT_SEND_AUTH_INFO_ERROR, {
 			tr_GSUP_IE_IMSI(imsi), tr_GSUP_IE_Cause(cause) });