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The Pennsylvania Supreme Court ruled Monday that the Republican-drawn state congressional map is illegally gerrymandered to benefit the GOP, ordering new maps ahead of the 2018 midterm elections. The decision in one of the country’s most closely watched redistricting battles will provide a boost to Democrats seeking to retake the House of Representatives by giving the party an opportunity to pick up Republican-held seats.

In 2011, Republicans who had swept into power in the wave election the previous November drew one of the country’s most aggressive gerrymanders. Now, Pennsylvania provides a unique opportunity to Democrats in 2018. As Mother Jones previously reported:

While Pennsylvania has roughly equal numbers of Democratic and Republican voters (Donald Trump won here by just 44,000 votes out of more than 6 million cast), for the last six years its congressional delegation has been made up of 13 Republicans and just five Democrats, who mostly represent Pittsburgh and Philadelphia. As Democrats scour the country for the approximately two dozen candidates and winnable districts they’ll need to take back the House, a redrawn congressional map in Pennsylvania could present the party with some prime opportunities to pick up seats.

Monday’s order requires the state’s Republican-led general assembly to draw a new map by February 9 and submit it to the governor—a Democrat—for approval. If the assembly fails to produce any map, or if the governor does not approve it, the state supreme court will produce its own map. The US Supreme Court could block Monday’s decision, but because it involves the interpretation of the Pennsylvania state constitution, such interference with the state court ruling is unlikely.