diff --git a/openbsc/include/openbsc/mgcp.h b/openbsc/include/openbsc/mgcp.h
index a1053be90..53a308152 100644
--- a/openbsc/include/openbsc/mgcp.h
+++ b/openbsc/include/openbsc/mgcp.h
@@ -118,5 +118,13 @@ void mgcp_free_endp(struct mgcp_endpoint *endp);
 struct msgb *mgcp_handle_message(struct mgcp_config *cfg, struct msgb *msg);
 struct msgb *mgcp_create_response_with_data(int code, const char *msg, const char *trans, const char *data);
 
+/* adc helper */
+static inline int mgcp_timeslot_to_endpoint(int multiplex, int timeslot)
+{
+	if (timeslot == 0)
+		timeslot = 1;
+	return timeslot + (31 * multiplex);
+}
+
 
 #endif
diff --git a/openbsc/src/bssap.c b/openbsc/src/bssap.c
index fac6c1f57..cdee92bc9 100644
--- a/openbsc/src/bssap.c
+++ b/openbsc/src/bssap.c
@@ -556,9 +556,7 @@ static int bssmap_handle_assignm_req(struct sccp_connection *conn,
 	bsc_schedule_timer(&msc_data->T10, GSM0808_T10_VALUE);
 
 	/* the mgcp call agent starts counting at one. a bit of a weird mapping */
-	if (timeslot == 0)
-		timeslot = 1;
-	port = timeslot + (31 * multiplex);
+	port = mgcp_timeslot_to_endpoint(multiplex, timeslot);
 	msc_data->rtp_port = rtp_calculate_port(port,
 						network->rtp_base_port);