diff --git a/library/GSM_Types.ttcn b/library/GSM_Types.ttcn
index b86bfd7..c7b7991 100644
--- a/library/GSM_Types.ttcn
+++ b/library/GSM_Types.ttcn
@@ -16,7 +16,7 @@
 	type integer GsmRxLev (0..63);
 	type integer GsmTsc (0..7) with { variant "FIELDLENGTH(8)" };
 	type uint32_t GsmTmsi;
-	type uint32_t GprsTlli;
+	type OCT4 GprsTlli;
 	type hexstring GsmMcc length(3);
 	type hexstring GsmMnc length(2 .. 3);
 	type uint16_t GsmLac;