Microsoft is starting to drop PCs from its Windows Insider testing program that are ineligible to upgrade to Windows 11. If you’ve been helping Microsoft test Windows 11 on a machine that doesn’t meet the minimum hardware requirements, you’ll likely see a message in Windows Update warning that you’ll need to reinstall Windows 10.

“Your PC does not meet the minimum hardware requirements for Windows 11,” says Microsoft’s warning. “Your device is not eligible to join the Windows Insider Program on Windows 11. Please install Windows 10 to participate in the Windows Insider Program in the Release Preview Channel.”

Windows 11 testers in both the Dev and Beta channels have started receiving the message on incompatible PCs this week, just as Microsoft has announced its October 5th release date for the upcoming OS. It’s something that Microsoft warned testers would happen at the beginning of the beta period of Windows 11, but it still highlights the often confusing minimum hardware requirements that Microsoft has set.

Windows 11 testers that have been running the OS on unsupported hardware will be able to use a workaround to install an ISO version of the final release. But Microsoft warns that devices in this unsupported state won’t be eligible for Windows Updates, and that could include security patches.

Microsoft recommends that Windows 11 testers that don’t meet the hardware minimums should install Windows 10, as this OS will be supported until 2025. Many Windows 11 testers, who are often loyal Microsoft enthusiasts, will still be left confused why their PC isn’t officially supported even though it has likely been running the OS just fine for months.

Microsoft has attempted to justify its Windows 11 minimum hardware requirements around a push for security and reliability, but it still leaves some PCs sold just a few years ago from being able to upgrade. Windows 11 raises the baseline of security to the CPU level, and Microsoft has been clear it wants to enforce or support Trusted Platform Module (TPM), UEFI Secure Boot, and virtualization-based security methods.

Windows 11 will now arrive on October 5th, and Microsoft will continue to release new Dev builds of the OS to testers. Android app integration isn’t arriving at launch but Windows Insider testers will get access in the coming months to the feature which relies heavily on modern hardware.