diff --git a/msc/BSC_ConnectionHandler.ttcn b/msc/BSC_ConnectionHandler.ttcn
index f141955..4351e06 100644
--- a/msc/BSC_ConnectionHandler.ttcn
+++ b/msc/BSC_ConnectionHandler.ttcn
@@ -1605,6 +1605,10 @@
 		var BSSMAP_IE_SpeechCodec codec;
 		var BSSMAP_IE_Osmo_OsmuxCID osmuxCID;
 
+		if (not ispresent(bssap.pdu.bssmap.assignmentRequest.aoIPTransportLayer)) {
+			setverdict(fail, "MSC sent Assignment Request without AoIP Transport Layer IE");
+			mtc.stop;
+		}
 		if (not match(bssap.pdu.bssmap.assignmentRequest.aoIPTransportLayer, tla_ass1)
 		    and not match(bssap.pdu.bssmap.assignmentRequest.aoIPTransportLayer, tla_ass2)) {
 			log("Expected one of: 1:", tla_ass1, " 2:", tla_ass2);