President Donald Trump said there is a “rigged election in waiting” in response to reports this week that some North Carolina residents received two absentee ballots.

The ballot duplication incident occurred in Mecklenburg County, where election officials told the Associated Press that fewer than 500 voters received identical ballots in the mail.

“Some people in the Great State of North Carolina have been sent TWO BALLOTS,” Trump tweeted on Thursday. “RIGGED ELECTION in waiting!”

The problem with the ballots began when some intended for voters in Matthews were printed with the wrong names, according to the AP. During the reprinting process, some of the voters on the absentee ballot recipient list received two, officials said.

Despite the error, Mecklenburg County Director of Elections Michael Dickerson told the AP that each ballot has its own mailing code, meaning it would be improbable that any voter would successfully cast two identical ballots.

North Carolina election officials reminded voters earlier this month that voting twice in an election breaks federal and state laws. Karen Brinson Bell, the executive director of the North Carolina State Board of Elections (NCSBE), issued a statement about double-voting attempts after Trump said during a visit to North Carolina on September 2 that mail-in voters should “check their vote” by also trying to vote in person. Trump has frequently spoken out against mail-in voting practices that he has said—without evidence—lead to voter fraud.

“It is illegal to vote twice in an election,” Bell’s statement said. The state’s board of elections enables registered voters to check the status of their ballots, and those who sign up to receive an absentee ballot but later decide they prefer to vote in person can throw the mailed ballot away and do so, she added.

“The State Board office strongly discourages people from showing up at the polls on Election Day to check whether their absentee ballot was counted,” Bell said. “That is not necessary, and it would lead to longer lines and the possibility of spreading COVID-19.”

The state’s attorney general, Josh Stein, also issued a statement earlier this month in response to the president’s comments, which he said were “deeply troubling.”

“North Carolina’s election system is strong,” Stein’s statement said. “It ensures that every eligible voter can vote easily, safely, securely, and only once, whether they choose to do so by mail or in person during our 17 days of early voting or on Election Day.”

When contacted for comment, the NCSBE referred Newsweek to a statement Bell issued Thursday about the ballot issue in Mecklenburg County.

“North Carolina’s statewide election management system will not allow a voter to vote twice in an election,” Bell’s statement said. “Each absentee voter has a unique identifier barcode for their return application, and the state system will not permit two ballots from the same person to be accepted or counted. Once one ballot is returned and accepted, the voter’s record reflects that he or she has already voted. Therefore, if that voter returned another ballot, it would not count.”

More than 7.1 million people were registered to vote in North Carolina by mid-September, and more than 837,000 of those requested absentee ballots by September 15, according to the NCSBE’s tallies. The NCSBE sent out about 817,000 ballots to state residents by mid-September, with about 88,000 of those returned by Thursday, Bell said.

Like many other states, North Carolina expanded mail-in voting access for this year’s election in light of the threats posed by the coronavirus pandemic. Those interested in voting by mail can request an absentee ballot up until October 27, according to the NCSBE.

Update (9/17/2020, 6:20 p.m. ET): This article has been updated to include a statement from the North Carolina state Board of Elections.