Microsoft is working to unify its desktop, mobile, and gaming platforms, but one vocal critic thinks this could come with some frightening consequences for the open legacy of the PC.

Tim Sweeney is not giving up his fight with Microsoft over what he argues is the closed nature of the Universal Windows Platform. During a fireside chat today at the GamesBeat Summit in Sausalito, California, the Epic Games founder and overseer of the Unreal Engine game-making tool also pushed¬†back against critics of his own who think he’s exaggerating the threat of UWP. But the industry veteran claimed that we’ve seen companies make these kinds of moves before, and he wants to stop it now before it’s too late.

“Microsoft has been taking a series of steps for a while now to close down the Windows ecosystem,” said Sweeney. “They can’t do it all at once, because there would be an industry uproar. But one little step at a time, they’re trying to take it all over. UWP is another step in that direction.”

UWP is a way for developers to build an app or game once and then deploy it for Windows 10, Windows Mobile, or Xbox One. This could simplify development¬†for a lot of studios, but Sweeney argues that you can’t release a UWP app without getting an approval from Microsoft. Additionally, end users cannot install UWP programs without first turning off a security feature that gives some dire warnings that may scare off some consumers. Microsoft has countered these concerns with claims that UWP is open, but Sweeney is worried this could limit the potential for Epic (and other companies) to successfully build up an audience for something like the Epic Games Launcher. That product is a way for his company to directly connect with its customers, and if it were a UWP app, Epic would have to share its revenues with Microsoft.

Today, anyone can still install the Epic Games Launcher without issue, and this has led to the claims that Sweeney is speaking about some hypothetical threat that may never end up coming to pass. In response to that, Sweeney shared the fable about a boiling frog.

“If you throw a frog in boiling water, he’ll just hop out,” Sweeney said. “But if you put him in warm water and slowly amp up the temperature, he won’t notice and end up boiled.”

He thinks that UWP is the warm water that’ll end up boiling his company out of the market.

“Look at Facebook,” Sweeney said. “Every company moved their brand presence to Facebook. They started sending out their consumer messaging on [that platform]. Now, you have to pay [Facebook] to send out your messages to people who chose to follow you. A boiling frog.”