Maryland’s top elections official, Jared DeMarinis, has confirmed that a coding error by a state vendor resulted in some voters receiving the wrong mail-in ballots ahead of the June 23 primary election.

According to DeMarinis, the issue was related to party affiliation coding and led the state to send more than 447,000 replacement ballots. He stated that the problem was caused by a vendor error and that safeguards have been put in place to prevent it from happening again.

The acknowledgment comes after widespread concern from voters who reported receiving incorrect ballots.