Slack, the chat app for businesses that became the fastest startup to ever achieve a $1 billion valuation, has a big problem:

The emoji for "hamburger" obviously shows a picture of a cheeseburger.

Just look at this:

While some Business Insider staffers thought the yellow patch might be mustard, the angle definitely suggests cheese.

This issue was first identified by Jon Hendren, a man who works in marketing for a startup called Scriptrock, but is perhaps better known by his popular Twitter account "@fart."

Slack security engineer Ryan Huber responded to Hendren's bug report with the confirmation that this was a serious security issue, since it means that Slack users could accidentally promise to buy one another a hamburger, but end up on the hook for a pricier cheeseburger.

"One might argue that the compound effect of this blunder could result in tens of dollars of losses across Slack's userbase," Huber wrote.

In exchange for pointing out this issue, Slack paid out a bounty of $12.50, enough for Hendren to buy "a reasonably priced hamburger or cheeseburger."

"Cheeseburger," said Slack CEO Stewart Butterfield when reached for comment.

You can see the full exchange on Twitter below: