diff --git a/msc_tests/BSC_ConnectionHandler.ttcn b/msc_tests/BSC_ConnectionHandler.ttcn
index 39acfb7..ee0e0ae 100644
--- a/msc_tests/BSC_ConnectionHandler.ttcn
+++ b/msc_tests/BSC_ConnectionHandler.ttcn
@@ -149,9 +149,15 @@
 	}
 
 	if (expect_auth) {
+		var OCT16 rand := 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'O;
+		var OCT4 sres := 'bbbbbbbb'O;
+		var GSUP_IE auth_tuple := valueof(ts_GSUP_IE_AuthTuple2G(rand, sres,
+									 'cccccccccccccccc'O));
 		GSUP.receive(tr_GSUP_SAI_REQ(g_pars.imsi));
-		/* FIXME */
-		//GSUP.send(tr_GSUP_SAI_RES());
+		GSUP.send(ts_GSUP_SAI_RES(g_pars.imsi, auth_tuple));
+
+		BSSAP.receive(tr_PDU_DTAP_MT(tr_ML3_MT_MM_AUTH_REQ(rand)));
+		BSSAP.send(ts_PDU_DTAP_MO(ts_ML3_MT_MM_AUTH_RESP_2G(sres)));
 	}
 
 	/* Expect MSC to perform LU with HLR */
diff --git a/msc_tests/MSC_Tests.ttcn b/msc_tests/MSC_Tests.ttcn
index dea27a7..15ffc20 100644
--- a/msc_tests/MSC_Tests.ttcn
+++ b/msc_tests/MSC_Tests.ttcn
@@ -418,6 +418,18 @@
 	vc_conn.done;
 }
 
+private function f_tc_lu_imsi_auth_tmsi(charstring id, BSC_ConnHdlrPars pars) runs on BSC_ConnHdlr {
+	g_pars := pars;
+	f_perform_lu(true, true, true);
+}
+testcase TC_lu_imsi_auth_tmsi() runs on MTC_CT {
+	var BSC_ConnHdlr vc_conn;
+	f_init();
+
+	vc_conn := f_start_handler(refers(f_tc_lu_imsi_auth_tmsi), testcasename(), 5);
+	vc_conn.done;
+}
+
 
 /* Send CM SERVICE REQ for IMSI that has never performed LU before */
 private function f_tc_cmserv_imsi_unknown(charstring id, BSC_ConnHdlrPars pars)