diff --git a/openbsc/tests/bsc-nat/bsc_nat_test.c b/openbsc/tests/bsc-nat/bsc_nat_test.c
index e9567c7..6f51707 100644
--- a/openbsc/tests/bsc-nat/bsc_nat_test.c
+++ b/openbsc/tests/bsc-nat/bsc_nat_test.c
@@ -630,7 +630,7 @@
 		char *input = strdup(orig);
 
 		output = bsc_mgcp_rewrite(input, strlen(input), 0x1e,
-					  ip, port, 0, &payload_type);
+					  ip, port, -1, &payload_type);
 
 		if (payload_type != -1) {
 			fprintf(stderr, "Found media payload type %d in SDP data\n",