A new survey of local election officials finds that it was extremely rare for non-citizens to vote in the 2016 election, casting even more doubt on President Donald Trump’s unfounded claim that millions of people cast illegal ballots last year.

Researchers from the Brennan Center for Justice interviewed local election officials in 42 jurisdictions across 12 states and found there’d been about 30 instances of suspected non-citizens voting. That’s out of 23.5 million ballots cast. The questionable votes accounted for just 0.0001 percent of the total number of votes in those jurisdictions.

The report focuses on counties where there are more than 100,000 adult non-citizens, as well as diverse areas with large populations in California, Virginia and New Hampshire, all states that Trump singled out for voter fraud.

The results are consistent with post-election audits that have shown voter fraud and instances of non-citizen voting to be vanishingly rare. In North Carolina, where 4.8 million ballots were cast, officials found just 41 suspected cases of non-citizens voting. Nevada Secretary of State Barbara Cegavske (R) has said she believes up to 21 non-citizens could have voted for president in the state, where there are more than 1.4 million active voters. In Ohio, Secretary of State Jon Husted (R) said that 82 non-citizens voted “in at least one election” (he did not say when).

Trump has said he believes between 3 and 5 million people voted illegally in the 2016 election. He has not provided any evidence for this claim, and has pledged a national probe into voter fraud. Civil rights groups are also suing Kansas over a law that requires people to prove they are U.S. citizens in order to vote.

When non-citizens do vote, it is often out of confusion or a failure to understand voting procedures, the Brennan Center report notes. Federal law requires the Department of Motor Vehicles to allow people to register to vote, and a non-citizen might unintentionally get added to the voter rolls if they don’t fully understand all the forms they’re filling out. In other cases, a canvasser might misinform a non-citizen of the law and tell them they are eligible to vote.

“Sometimes a voter won’t understand that they’re completing a voter registration application,” Lynn Ledford, the voter registration and election director in Gwinnett County, Georgia, told the Brennan Center researchers. “They will come and self-report and explain their accident. Then we give them a confirmation in writing that they have been removed and take them off the rolls.”

It’s also easy for U.S. citizens to get flagged as non-citizens and ineligible voters. Jacquelyn Callanen, elections administrator in Bexar County, Texas, told the researchers that sometimes citizens will say they are non-citizens in an attempt to get out of jury duty, and will subsequently be flagged for an investigation. Sometimes people simply forget to check a box indicating they are a citizen when they fill out a driver’s license form. Data can also be unreliable: In North Carolina, officials found that 34 people flagged as non-citizens were in fact citizens.