The change will prohibit superdelegates from voting for president at the party’s 2020 convention, unless the outcome is already assured or it deadlocks, which hasn’t happened in decades. The vast majority of superdelegates sided with Hillary Clinton over Sanders in their primary fight two years ago.

“Today’s decision by the DNC is an important step forward,” Sanders said in a statement. “This has been a long and arduous process, and I want to thank Tom Perez and all of those who made it happen.”

The new rules will also make caucuses more accessible by requiring state parties to accept absentee votes, addressing concerns that the caucuses are less democratic than primaries because they require people to physically attend the events in order to participate in the presidential nominating process in their state.