An error at California’s Department of Motor Vehicles caused more than a thousand people, including some who were not U.S. citizens, to be incorrectly registered to vote, state officials said Monday.

The DMV admitted that a “processing error” at agency field offices resulted in as many as 1,500 people being added to voter rolls between April 23 and Sept. 25.

The widespread glitch was discovered after Randall Marquis, a Canadian citizen and legal U.S. resident living in California, notified the DMV he had received a piece of mail from the agency saying he was registered to vote. In response to Marquis’ alert, the agency ordered an internal audit and discovered hundreds of similar cases.

“This error occurred when DMV technicians processed customer requests at field offices to change voter eligibility responses on driver license applications,” the DMV wrote in a letter to California Secretary of State Alex Padilla, according to the San Francisco Chronicle. “Due to the order in which the change was processed, the customer’s initial responses were retained instead of the correct and revised responses.”

The DMV said the improper registrations were made “through no fault of the customer.” None of the people who were registered to vote due to the error were illegal immigrants, the agency added.

“We have worked quickly with the Department of Technology to correct these errors and have also updated the programming and added additional safeguards to improve this process,” DMV Director Jean Shiomoto said in a statement Monday, according to ABC News.

The spate of improper registrations was the second major statewide error at the California DMV in the last two months. The agency admitted in early September that it had mishandled about 23,000 voter registrations by assigning them to the wrong political party or mislabeling vote-by-mail preferences.

Padilla said Monday he was “deeply frustrated and disappointed” by the errors at the DMV. He called on the agency to hire an outside consultant to help shore up its voter registration process.

An audit of California’s DMV voter registration program—commonly known as “motor voter”—is likely to turn up more instances of mistaken registration, according to the Public Interest Legal Foundation, a nonprofit that investigates election integrity issues. A Public Interest Legal Foundation report released in August found that hundreds of noncitizens were recently purged from voter rolls in three major California counties, most of them after having registered through the motor voter program.

“There can be much more to come on this front, given Secretary Padilla’s quick call for an audit and quoted claims from noncitizens caught in the system,” Public Interest Legal Foundation spokesman Logan Churchwell told The Daily Caller News Foundation. “Too many noncitizens learn of … their unlawful registrations from federal authorities during immigration procedures thanks to sloppy motor voter enforcement like seen here. We’ve seen thousands document those rude awakenings across the country.”

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