If a unicorn farts in a Tesla, should someone pay?

That’s the question at the heart of a dispute between Tesla CEO Elon Musk and a Colorado artist who claims Tesla appropriated and failed to pay for a farting-unicorn image he created on a mug, according to a new report.

The 61-year-old potter had been excited last year when Musk tweeted out a photo of his work, saying it might be his “favorite mug ever,” The Guardian reported Wednesday.

The Tesla CEO’s admiration is not altogether surprising, as he makes electric cars and artist Tom Edwards’ unicorn farts electricity.

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But then Edwards saw that Musk had tweeted a copy of the cartoonish mythical creature for apparent commercial purposes, using it to promote a feature allowing people to draw on a Tesla car’s touchscreen, according to The Guardian.

It seemed a small enough thing to overlook, but then the artist discovered that the Palo Alto firm’s version of his image was appearing in Tesla’s operating system as a small icon, and had been used in a company Christmas card, the paper reported.

“It’s part of their branding now,” Edwards told The Guardian.

“I love the fact that it’s in the cars, but I just want them to do the right thing and pay me adequately for it. Elon Musk can be a hero for standing up for artists’ rights.”

Musk instead stood up for his company’s right to use the image.

“Was actually someone else’s drawing of a unicorn on hidden Tesla sketch pad app & we gained no financial benefit,” Musk tweeted Tuesday. By Thursday, it appeared Musk’s tweets concerning the dispute had been deleted.

“Have asked my team to use a diff example going forward. He can sue for money if he wants, but that’s kinda lame. If anything, this attention increased his mug sales.”