diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index f40b19e..aa627b7 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -1852,6 +1852,7 @@
 private function f_tc_assignment_csd(charstring id) runs on MSC_ConnHdlr {
 	var template PDU_BSSAP exp_compl := f_gen_exp_compl();
 	var PDU_BSSAP ass_cmd := f_gen_ass_req();
+	var SDP_FIELD_PayloadType pt_csd := PT_CSD;
 
 	ass_cmd.pdu.bssmap.assignmentRequest.channelType := valueof(ts_BSSMAP_IE_ChannelTypeCSD);
 	ass_cmd.pdu.bssmap.assignmentRequest.codecList := valueof(ts_BSSMAP_IE_CodecList({ts_CodecCSData}));
@@ -1859,6 +1860,11 @@
 	ass_cmd.pdu.bssmap.assignmentRequest.channelType.speechId_DataIndicator := GSM0808_DATA_RATE_TRANSP_4k8;
 
 	f_establish_fully(ass_cmd, exp_compl);
+
+	if (g_media.bts.rtp_pt != enum2int(pt_csd)) {
+		Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail, log2str("unexpected RTP payload type: ", g_media.bts.rtp_pt));
+	}
+
 	f_perform_clear();
 }
 testcase TC_assignment_csd() runs on test_CT {