If your Windows 11 PC tried to install the May 2026 update and rolled back with error 0x800f0922, you're not alone. Microsoft confirmed on May 16 that KB5089549 — the May Patch Tuesday cumulative update — is failing on machines with very little free space in a hidden boot partition called the EFI System Partition. An emergency server-side fix is already rolling out, and most home users won't need to do anything except reboot and try again.
What's actually going wrong
The May 2026 cumulative update for Windows 11 24H2 and 25H2 is KB5089549, released on May 12. On some machines, it fails during the installation step and rolls back with the message "Something didn't go as planned — undoing changes. Please keep your computer on."
The installation fails with error code 0x800f0922, and the CBS log shows "ServicingBootFiles failed" entries indicating insufficient free space on the EFI System Partition. That EFI partition is a small hidden area Windows uses during boot — typically only 100 MB. That 100 MB can run out when OEM firmware updates leave bulky files behind or when multiple Windows versions or even Linux have been installed, and if free EFI storage drops below 10 MB the update can fail.
Microsoft's fix is already going out automatically
Microsoft has patched the problem server-side using Known Issue Rollback (KIR). The resolution has already propagated automatically to consumer devices and non-managed business devices, and restarting your Windows device might help the resolution apply more quickly.
In plain English: reboot your PC a couple of times, then try Windows Update again. For most home users on a standard Dell, HP, Lenovo, or custom-built Windows 11 PC, that's the entire fix.
If the update still won't install after a few reboots, Microsoft's other option is more involved. There are two ways to get it through, and one tells Windows not to expect any spare room in that hidden partition. That involves a registry edit and isn't something most people should try at the kitchen table.
When this gets serious: HP laptops and unbootable PCs
Most failed installs roll back cleanly and leave your PC working normally — the update just didn't take. The dangerous cases are rare but real. The problem cases are mainly HP laptops and other devices where the EFI partition has almost no space left; Windows needs to write new boot files as part of installing the update, and on a handful of HP devices this has left the PC unbootable rather than rolling back cleanly.
If your PC won't boot at all after this update, that's a recovery job — not a casual fix. Rebuilding a broken boot environment from a recovery USB requires the right tools and a careful hand, and it's the kind of problem our desktop and PC repair bench sees regularly after botched updates. If the drive itself has problems on top of a failed update, you may also need file recovery from the dead drive before reinstalling Windows.
How to check if you're affected before installing
You can't go to File Explorer and right-click one of the volumes to find out the current EFI storage space because Windows automatically hides the partition for safety reasons, but you can use a PowerShell script to peek inside. If you're comfortable opening PowerShell as administrator, Microsoft has published the exact command to check your EFI partition's free space.
If you'd rather not touch PowerShell — fair — the practical advice is simple: let Windows Update try once, and if it rolls back, reboot twice and try again now that the Known Issue Rollback has shipped. If KB5089549 fails to install, Windows 11 will usually revert automatically after the error appears, and users can then try running the update again through Windows Update.
One unrelated bug worth knowing about
Separately, Microsoft also acknowledged a GPU driver downgrade issue tied to Windows Update — not specific to the May patch, but on the radar this week. Microsoft finally confirmed that Windows 11 downgrades GPU drivers on OEM devices and is planning to launch a partial fix by Q4 2026. This affects anyone on Windows 11 who has manually installed a graphics driver from Nvidia, AMD, or Intel's website; if Windows has always handled your drivers automatically you're almost certainly fine, and the people who notice are gamers and video editors who keep their GPU drivers current.
If your games suddenly feel off after a Windows update, that's worth checking — and it's the kind of thing our gaming PC techs sort out routinely.
What This Means for York, PA
For York County customers: if your Windows 11 PC keeps trying to install the May update and rolling back, give it a couple of reboots first — Microsoft's automatic fix should reach you within a few days. If your computer won't boot at all after the update, don't keep poking at it. Bring it to our shop at 2069 Carlisle Rd and we'll get the boot environment rebuilt without losing your files.
Sources
- Microsoft confirms Windows 11 KB5089549 issues due to low storage, says it's rolling out an emergency patch
- May 12, 2026—KB5089549 (OS Builds 26200.8457 and 26100.8457) - Microsoft Support
- Windows 11's May update is causing install failures and slow internet — here's what we know
- Microsoft is working on a fix to downgraded GPU drivers in Windows Update