LINCOLN, Neb. (AP) — The Nebraska secretary of state’s office says ballot-counting equipment used in the May primary has passed an election audit.

The mandatory audit is conducted following each statewide election to confirm the accuracy and reliability of those machines. Secretary of State John Gale said Wednesday that only one issue was detected in Greeley County, not because of the equipment, but because of mistakes made by two voters. Those voters marked their ballots with an “X” instead of filling in ovals as required.

Officials say 36 of the 1,384 precincts in Nebraska were randomly chosen as part of the audit. In those precincts, election officials compared results generated by optical scanning equipment with hand counted ballots.