No matter who wins the U.S. Senate runoff, the results will be double-checked in some counties in Georgia.

A memo sent by the secretary of state’s office this week asks county election directors to conduct a post-election audit that will count a sample of paper ballots by hand and then compare the results to computer tabulations.

The audit is optional, with each of the state’s 159 county election offices able to decide whether they want to participate.

Democratic U.S. Sen. Raphael Warnock faces Republican Herschel Walker in the runoff. The last day of early voting was Friday, and election day is Tuesday.

State Elections Director Blake Evans urged counties to conduct the audit because he said its benefits outweigh the costs to local governments.

“I believe that an audit will bring additional public confidence to the outcome of the election. My hope is that all counties choose to participate,” Evans wrote in a message to county election officials.

State law requires an audit of one race after each general election, but audits aren’t mandated after runoffs.

Following last month’s election, an audit of a sample of 231,000 ballots cast counted 21 more votes for Republican Secretary of State Brad Raffensperger and 18 fewer votes for Democrat Bee Nguyen. Raffensperger won the race by 9.3 percentage points, the largest margin of any statewide candidate.

The audit of the U.S. Senate runoff will be conducted Dec. 14 and Dec. 15. The deadline for Raffensperger to certify the election is Dec. 23.