diff --git a/openbsc/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index dd29c7aa5..02290231d 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -54,6 +54,16 @@ enum {
 	NAT_CON_TYPE_OTHER,
 };
 
+/*
+ * Is this terminated to the MSC, to the local machine (release
+ * handling for IMSI filtering) or to a USSD provider?
+ */
+enum {
+	NAT_CON_END_MSC,
+	NAT_CON_END_LOCAL,
+	NAT_CON_END_USSD,
+};
+
 /*
  * Per BSC data structure
  */
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index d38256587..e395ba516 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -399,7 +399,7 @@ static void bsc_send_con_release(struct bsc_connection *bsc, struct sccp_connect
 		ipaccess_prepend_header(rlsd, IPAC_PROTO_SCCP);
 		queue_for_msc(con->msc_con, rlsd);
 	}
-	con->con_local = 1;
+	con->con_local = NAT_CON_END_LOCAL;
 	con->msc_con = NULL;
 
 	/* 2. release the BSC side */
@@ -465,7 +465,7 @@ static void bsc_send_con_refuse(struct bsc_connection *bsc,
 
 		/* declare it local and assign a unique remote_ref */
 		con->con_type = NAT_CON_TYPE_LOCAL_REJECT;
-		con->con_local = 1;
+		con->con_local = NAT_CON_END_LOCAL;
 		con->has_remote_ref = 1;
 		con->remote_ref = con->patched_ref;
 
@@ -942,7 +942,7 @@ static int forward_sccp_to_msc(struct bsc_connection *bsc, struct msgb *msg)
 
 					/* hand data to a side channel */
 					if (bsc_check_ussd(con, parsed, msg) == 1) 
-						con->con_local = 2;
+						con->con_local = NAT_CON_END_USSD;
 
 					/*
 					 * Optionally rewrite setup message. This can
@@ -1414,7 +1414,7 @@ int bsc_close_ussd_connections(struct bsc_nat *nat)
 {
 	struct sccp_connections *con;
 	llist_for_each_entry(con, &nat->sccp_connections, list_entry) {
-		if (con->con_local != 2)
+		if (con->con_local != NAT_CON_END_USSD)
 			continue;
 		if (!con->bsc)
 			continue;