diff --git a/pcu/GPRS_Components.ttcn b/pcu/GPRS_Components.ttcn
index 983ae8f..aaec6d3 100644
--- a/pcu/GPRS_Components.ttcn
+++ b/pcu/GPRS_Components.ttcn
@@ -1175,9 +1175,8 @@
 	rr_pag_req1 := data_msg.rr_msg;
 	log("Rx Paging Request Type1: ", rr_pag_req1);
 
-
-	/* First 3 bytes contain IMSI suffix to calculate paging group: */
-	imsi_suff_octstr := substr(data_msg.raw.data, 0, 3);
+	/* The last 3 digits of the IMSI are used to calculate paging group: */
+	imsi_suff_octstr := substr(char2oct(data_msg.imsi), lengthof(data_msg.imsi) - 3, 3);
 	pag_group_rx := str2int(oct2char(imsi_suff_octstr[0])) * 100 +
 			str2int(oct2char(imsi_suff_octstr[1])) * 10 +
 			str2int(oct2char(imsi_suff_octstr[2]));