diff --git a/msc/MSC_Tests.ttcn b/msc/MSC_Tests.ttcn
index 508acdd..529a396 100644
--- a/msc/MSC_Tests.ttcn
+++ b/msc/MSC_Tests.ttcn
@@ -3504,7 +3504,7 @@
 runs on BSC_ConnHdlr {
 	f_init_handler(pars);
 
-	f_ran_register_imsi(g_pars.imsi, 'FFFFFFFF'O);
+	f_ran_register_imsi(g_pars.imsi, g_pars.tmsi);
 	f_create_gsup_expect(hex2str(g_pars.imsi));
 
 	/* Perform location update */
@@ -3568,7 +3568,7 @@
 	/* Perform location update */
 	f_perform_lu();
 
-	f_ran_register_imsi(g_pars.imsi, 'FFFFFFFF'O);
+	f_ran_register_imsi(g_pars.imsi, g_pars.tmsi);
 	f_create_gsup_expect(hex2str(g_pars.imsi));
 
 	/* Request referencing a non-existing SS session */
@@ -3610,7 +3610,7 @@
 	/* Perform location update */
 	f_perform_lu();
 
-	f_ran_register_imsi(g_pars.imsi, 'FFFFFFFF'O);
+	f_ran_register_imsi(g_pars.imsi, g_pars.tmsi);
 	f_create_gsup_expect(hex2str(g_pars.imsi));
 
 	var template (value) GSUP_PDU gsup_req := ts_GSUP_PROC_SS_REQ(
@@ -3670,7 +3670,7 @@
 	/* Perform location update */
 	f_perform_lu();
 
-	f_ran_register_imsi(g_pars.imsi, 'FFFFFFFF'O);
+	f_ran_register_imsi(g_pars.imsi, g_pars.tmsi);
 	f_create_gsup_expect(hex2str(g_pars.imsi));
 
 	/* PROC_SS_REQ initiates a mobile-originated SS/USSD session */