DENVER (AP) — Some early voters in Denver have been marking more than one presidential candidate on their ballots, invalidating their votes in a tight race.

Denver election worker Ron Weil said that he’s seen hundreds of early voter ballots that have multiple votes for the 16 candidates listed on Colorado’s ballot.

Denver Elections spokesman Alton Dillard said Wednesday that the number of presidential overvotes won’t be known until votes are tabulated next week. Officials do know that about 2.5 percent of 80,000 early ballots cast were initially rejected and had to be duplicated by election workers because of problems including overvoting as well as ballot damage. Workers can’t correct for overvotes because there’s no way of knowing the voter’s intent but votes in other races are still valid and counted.

(© Copyright 2012 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)