A federal judge in Georgia on Monday ordered two counties to reverse a decision removing more than 4,000 voters from the rolls ahead of the Jan. 5 runoff elections that will decide control of the U.S. Senate.

The judge, Leslie Abrams Gardner — the sister of former gubernatorial candidate Stacey Abrams, a prominent ally of President-elect Joe Biden who has led voter registration efforts across the state — concluded that the counties appeared to have improperly relied on unverified change-of-address data to invalidate registrations in the two counties.

The bulk of the registrations that the counties sought to rescind, more than 4,000, were in Muscogee County, which Biden won handily in November. An additional 150 were from Ben Hill County, which Trump won by a wide margin.

The suit, brought by Majority Forward, represented by National Democratic Party attorney Marc Elias, followed an effort to challenge the lengthy roster of voters simply because their registrations appeared to match U.S. Postal Service change-of address records. Voting officials in the two counties agreed to remove the voters, despite warnings from Democrats that such postal data is not a reliable or conclusive indicator that a voter has given up their local residence.

After Gardner’s ruling, Elias hailed the decision as a “blow to GOP voter suppression.”

“We continue to monitor how other Georgia counties respond to the suppression scheme,” he added. “Where necessary, we will sue and we will win.”