As many as 160 people who voted using the touchscreen at the Mills College Vote Center in Oakland took their ballots with them when they left, apparently believing the printout was a “receipt,” instead of depositing them in the official vote trolley, according to Alameda County Registrar Tim Dupuis.

Dupuis said the county was able to retrieve 22 of the missing ballots, which had a distinct watermark for validation. He said the number of unrecovered ballots was not enough to affect any of the races. About 300 voters used the touchscreen at Mills College.

Dupuis said nearly 800,000 of the county’s 966,000 registered voters (81%) cast ballots in this year’s election. Every registered voter received a mail-in ballot, which could be dropped off at one of 100 vote centers, 66 official drop boxes, or a U.S. mailbox. Dupuis said fewer than 57,000 people opted to vote in person.