diff --git a/sgsn/SGSN_Tests.ttcn b/sgsn/SGSN_Tests.ttcn
index c6e22ccc6..b79aae40b 100644
--- a/sgsn/SGSN_Tests.ttcn
+++ b/sgsn/SGSN_Tests.ttcn
@@ -768,7 +768,9 @@ function f_upd_ptmsi_and_tlli(OCT4 p_tmsi, integer ran_index := 0) runs on BSSGP
 function f_process_attach_accept(PDU_GMM_AttachAccept aa, integer ran_index := 0) runs on BSSGP_ConnHdlr {
 	/* mandatory IE */
 	var hexstring aa_plmn := f_RAI_to_plmn_hexstr(aa.routingAreaIdentification);
-	if (not (g_pars.bssgp_cell_id[ran_index].ra_id.lai.mcc_mnc == aa_plmn)) {
+	/* we cannot use ran_index here, as it would overflow the cell_id object, since ran_idx > NUM_GB
+	 * indicates an Iu RAN connection.  All cells are expected to run the same MCC/MNC anyway... */
+	if (not (g_pars.bssgp_cell_id[0].ra_id.lai.mcc_mnc == aa_plmn)) {
 		  setverdict(fail, "mismatching PLMN in Attach Accept: " & hex2str(aa_plmn)
 				   & "; expected " & hex2str(g_pars.bssgp_cell_id[ran_index].ra_id.lai.mcc_mnc));
 		  mtc.stop;