The Field Museum on Thursday announced a promotion offering free admission with proof of voting.

The bad news? That offer was illegal.

“The intention is golden. But under the law, you can’t offer anything of value in connection with registering to vote or voting,” said Jim Allen, spokesman for the Chicago Board of Election Commissioners.

The good news? Now the free admission offer will be extended to all Illinois residents, regardless of whether or not they’ve got an “I Voted” sticker.

Related: Check out our Illinois Voting Guide

“Oh, what the heck,” the museum announced after a nitpicking Chicago Sun-Times reporter inquired about the potential felony. “Field Museum free to all IL residents Nov. 6, even if you don’t vote.”

Field Museum spokeswoman Kate Golembiewski called it a mistake, saying they “still hope people research the issues that matter to them and make their voices heard.”

The exterior of The Field Museum of Natural History at 1400 S Lake Shore Drive in Chicago.

The exterior of The Field Museum of Natural History at 1400 S Lake Shore Drive in Chicago.

In a morning press release, museum officials had said they were “encouraging people to vote” with free passes on Tuesday and Wednesday for people with proof they’d voted.

“Voting matters. Every day in the news, we can read about what’s at stake for the planet and the people on it, especially humanity’s most vulnerable,” Field Museum president Richard Lariviere said. “Now is the time for everyone to make their voice heard.”

The not-for-profit museum’s statement noted: “We can’t tell you what or who to vote for, but we can share what’s important to us. Our mission is to ensure a brighter future, rich in nature and culture. Building such a future relies on fighting climate change, safeguarding scientific research, and celebrating diversity.”

Under state election law, giving or lending “any money or other valuable consideration to any other person to influence such other person to vote or to register to vote,” is considered a felony. It’s also prohibited by federal election law, punishable by up to five years in prison and a $10,000 fine.

Illinois State Board of Elections spokesman Matt Dietrich said the Field Museum’s offer was a “technical violation,” though you’d be hard-pressed to find a prosecutor willing to press charges.

The museum noted that they’re “in good company with this mistake,” as dozens of businesses across the country roll out civic-minded sales around election season. It’s perfectly legal in some states, as long as no federal candidates are on the ballot.

“We run into this just about every election year,” Allen said. “Institutions with the purest, most patriotic motivations put together an offer of a discount or a freebie. But they have to pull it back.”

Free days at the Field Museum are also scheduled for Illinois residents on Nov. 11 and 18.