diff --git a/openbsc/src/rtp_proxy.c b/openbsc/src/rtp_proxy.c
index 0293812..0f4e327 100644
--- a/openbsc/src/rtp_proxy.c
+++ b/openbsc/src/rtp_proxy.c
@@ -666,9 +666,10 @@
 }
 
 /* bind RTP/RTCP socket to application */
-int rtp_socket_upstream(struct rtp_socket *this, struct gsm_network *net, u_int32_t callref)
+int rtp_socket_upstream(struct rtp_socket *this, struct gsm_network *net,
+			u_int32_t callref)
 {
-	DEBUGP(DMUX, "rtp_socket_proxy(this=%p, callref=%lu)\n",
+	DEBUGP(DMUX, "rtp_socket_proxy(this=%p, callref=%u)\n",
 		this, callref);
 
 	if (callref) {