diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index 7ede318..dc8024a 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -319,6 +319,7 @@
 	net->msc_data->pong_timeout = 5;
 	net->msc_data->core_ncc = -1;
 	net->msc_data->rtp_payload = 126;
+	net->msc_data->rtp_base = 4000;
 
 	gsm_net_update_ctype(net);