diff --git a/src/hlr.c b/src/hlr.c
index 504c8d2..4fc072f 100644
--- a/src/hlr.c
+++ b/src/hlr.c
@@ -53,8 +53,12 @@
 	rc = db_get_auc(g_dbc, gsup->imsi, gsup_out.auth_vectors,
 			ARRAY_SIZE(gsup_out.auth_vectors),
 			NULL /* gsup->rand_auts */, gsup->auts);
-	if (rc <= 0) {
+	if (rc < 0) {
 		gsup_out.message_type = OSMO_GSUP_MSGT_SEND_AUTH_INFO_ERROR;
+		gsup_out.cause = GMM_CAUSE_NET_FAIL;
+	} else if (rc == 0) {
+		gsup_out.message_type = OSMO_GSUP_MSGT_SEND_AUTH_INFO_ERROR;
+		gsup_out.cause = GMM_CAUSE_IMSI_UNKNOWN;
 	}
 
 	msg_out = msgb_alloc_headroom(1024+16, 16, "GSUP AUC response");