diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c b/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c
index d29ea9c..64f6d73 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_filter.c
@@ -163,7 +163,7 @@
 		LOGP(DNAT, LOGL_DEBUG,
 			"Blocking subscriber IMSI %s with CM: %d LU: %d\n",
 			imsi, cm, lu);
-		return -1;
+		return -4;
 	}