This article originally appeared on VICE US.
Donkey Kong is one of the most-loved and most-played arcade games of all time. It made Nintnedo a household name, and launched the character later known as Mario into pop-culture stardom. It also contained a bug that made the game easier for players, and which arcade owners had to pay $125 to fix.
In Donkey Kong, players maneuver Jumpman (proto-Mario) up a set of ladders with the goal of rescuing Pauline from the eponymous ape. Donkey Kong hurls barrels at Jumpman, which roll off the side of the platforms and occasionally down the ladders that Jumpman uses to ascend. The original North American release of the Donkey Kong arcade cabinet in July 1981 contained a bug, however, that made it so a skilled player could wait at the top of a ladder and the barrels would never come down. This allowed players in the know to take a breath, create opportunities to ascend, and ultimately keep playing without spending money.
This, of course, was bad for business.
Someone caught the glitch and the Lieberman Music Company (LMC)—Nintendo’s early arcade distributor—sent a letter out to arcade owners saying that all new Donkey Kong cabinets would patch out the ladder safety glitch. Arcade owners could also buy a kit to fix the problem on their current machines, but it would cost them $125. Supper Mario Broth, a site that catalogs obscure mario content, shared the letter on Twitter on Monday. It’s also saved on Arcade Archive, a site that preserves manuals and documents related to arcade games.
The letter made it clear that patching the ladder glitch would make the arcade owners money. “Based on our test results revenues have increased an average of 20 percent after installation of the speed up kits,” the letter said.
$125 may seem like a lot of money for a patch, but in 1981 fixing a bug wasn’t as simple as pushing out a software update. To fix the issue, LMC sent out four sticks of EPROM—a programmable computer chip—that Donkey Kong owners had to slot into the arcade cabinet’s system board.
Information about this glitch is scarce in part because it was caught early; the letter is dated December 11, 1981, just five months after the cabinet’s release in North America. It’s also similar to another ladder glitch that is still present in the NES release of Donkey Kong, which shipped in 1983 in Japan and 1986 in North America. That glitch lets players move down a ladder and skip most of the first level.
Today, video game companies regularly patch games with tweaks and improvements that may change how the game looks or plays. In online shooters, for example, a common tweak is making weapons stronger or weaker in order to shift the difficulty balance. Thankfully, gamers no longer have to wait for a kit in the mail to receive these updates, or pay extra for them.