Italy’s main political parties agreed to an electoral reform plan that was unveiled last week by the leader of the ruling Democratic Party, Matteo Renzi, and former prime minister Silvio Berlusconi, the leader of the opposition conservatives, but demanded changes to make it easier for smaller parties to enter parliament.

Under the reforms, a 4.5-percent threshold would be introduced for parties to enter parliament, down from the 5-percent threshold Berlusconi and Renzi has proposed.

The revisions would also increase the chance of a runoff being called between the two biggest parties, raising the minimum required to claim an outright victory from 35 to 37 percent of the votes. The winning party or bloc would automatically get a majority of the seats in the lower chamber.

A separate law would reduce the Senate, which currently has equal lawmaking powers to the lower chamber, to a regional assembly.

The reforms are designed to prevent a repeat of last year’s election when neither Renzi’s Democrats nor Berlusconi’s conservatives were able to secure majorities in both chambers of parliament. After months of bickering and talks, they formed a left-right coalition, unusual in Italy, that was weakened in November when Berlusconi’s party split and hardliners pulled out, continuing in opposition under the name Forza Italia.

Berlusconi’s former deputy, interior minister Angelino Alfano, founded a new party, Nuovo Centrodestra, which is still in coalition and supports the reforms.

The most recent opinion poll puts Forza Italia at almost 21 percent support while Nuovo Centrodestra would struggle to cross the 4.5-percent threshold. The separatist Lega Nord, Berlusconi’s ally, gets 5.8 percent support.

The Democratic Party is at 28 percent but its former Green and socialist party ally, Sinistra Ecologia Libertà, which does not support the government, would fail to reenter parliament with 3.3 percent of the votes. So would the centrists that supported former prime minister Mario Monti’s reelection last year.

Former comedian Beppe Grillo’s anti-establishment Five Star Movement is still supported by roughly a quarter of the Italian electorate. It has been critical of the proposed reforms even if they should allow it to win more seats in the next election.

The reforms should go to the lower house on Thursday but are not expected to be enacted before April.