diff --git a/library/GSM_Types.ttcn b/library/GSM_Types.ttcn
index b234bf4..54c2e98 100644
--- a/library/GSM_Types.ttcn
+++ b/library/GSM_Types.ttcn
@@ -29,6 +29,8 @@
 type hexstring GsmMnc length(2 .. 3);
 type uint16_t GsmLac;
 type uint16_t GsmCellId;
+type octetstring GroupCallRef length(1 .. 5);
+
 
 /* ARFCN with explicit band discrimination */
 type record GsmBandArfcn {