diff --git a/library/DIAMETER_Templates.ttcn b/library/DIAMETER_Templates.ttcn
index 4dd686a..b6723e7 100644
--- a/library/DIAMETER_Templates.ttcn
+++ b/library/DIAMETER_Templates.ttcn
@@ -625,7 +625,7 @@
 	}
 }
 template (value) GenericAVP ts_AVP_UserNameImsi(hexstring imsi) := ts_AVP_UserName(char2oct(hex2str(imsi)));
-template (present) GenericAVP tr_AVP_UserNameImsi(hexstring imsi) := tr_AVP_UserName(char2oct(hex2str(imsi)));
+template (present) GenericAVP tr_AVP_UserNameImsi(template (present) hexstring imsi := ?) := tr_AVP_UserName(char2oct_tmpl(hex2str_tmpl(imsi)));