diff --git a/src/rest.c b/src/rest.c
index 2b8fbaf..8191648 100644
--- a/src/rest.c
+++ b/src/rest.c
@@ -1337,6 +1337,14 @@ static int og_set_client_mode(struct og_dbi *dbi, const char *mac,
 
 		"WHERE ordenadores.mac='%s'", getenv("LANG"), mac);
 
+	if (!result) {
+		dbi_conn_error(dbi->conn, &msglog);
+		syslog(LOG_ERR, "failed to query database (%s:%d) %s\n",
+		       __func__, __LINE__, msglog);
+		og_dbi_close(dbi);
+		return -1;
+	}
+
 	if (dbi_result_get_numrows(result) != 1) {
 		dbi_conn_error(dbi->conn, &msglog);
 		syslog(LOG_ERR, "failed to query database (%s:%d) %s\n",