The parliament of Poland consists of an upper house – the Senate – and a lower house, the Sejm. Both houses are accommodated by the Sejm building complex in Warsaw. The parliament itself is without an official name; Poland's constitution refers only to the Sejm and the Senate. Members of both houses are elected by popular elections, usually held every four years. The Sejm has 460 members, while the Senate has 100 senators. To become law, a bill must first be approved by both houses. The Sejm can override a Senate refusal to pass a bill.