Steam will no longer allow games that enable NFT (non-fungible token) and cryptocurrency trading through the blockchain. Steam’s onboarding page for Steamworks users and partners now states that they shouldn’t publish “applications built on blockchain technology that issue or allow exchange of cryptocurrencies or NFTs” on Steam. The rule was added at some point after October 6th, according to a version of the page cached by Google.

Some developers have spoken out about the rule. SpacePirate Games, the studio behind a sci-fi action-adventure title called Age of Rust, said Valve was booting blockchain games off of Steam “because NFTs have value.” Some puzzles in Age of Rust, which is in development, will reward players with NFTs as achievements. “Steam’s point of view is that items have value and they don’t allow items that can have real-world value on their platform,” SpacePirate said. The developer plans to publish the game elsewhere.

It’s unclear how many games already on Steam will be affected. Searching for “NFT” and “crypto” turns up 14 and 64 results respectively. Not all of those necessarily allow real-world trading though. Crypto Mining Simulator, for instance, lets you pretend you’re mining cryptocurrency, which sounds like a barrel of laughs.

Engadget has contacted Steam for more details about this rule, including why it was brought in. NFT scams do exist, and unless you know what you’re doing, it’s not hard to get burned on crypto trading. That said, Valve does allow people to exchange virtual goods for Steam Wallet funds through the community market, so SpacePirate’s belief that Steam doesn’t permit items with real-world value doesn’t entirely hold water.