HARRISBURG, Pa. (AP) — Pennsylvania election officials say noncitizen immigrants illegally voted hundreds of times in elections spanning 18 years, though that may not be the full number.

State Department official Jonathan Marks told a state House committee Wednesday that an agency analysis found 544 ballots cast out of more than 93 million ballots from 2000 through 2017.

That’s one in every 172,000.

The department says those ballots were cast by noncitizen immigrants who reported themselves as having mistakenly registered. Pressed by Republican state lawmakers, the department says it’s looking into whether other noncitizen immigrants remain registered to vote.

Marks says a glitch that allowed many to inadvertently register will be fixed within several months.

The hearing came two weeks after Pennsylvania’s chief election official, Secretary of State Pedro Cortes, abruptly resigned without explanation.