May's Windows 11 update won't install? It's a tiny hidden partition, not your PC

If your Windows 11 PC choked on May's update, you weren't alone. Microsoft confirmed that the May 2026 security update, KB5089549, was failing on some machines - grinding to a halt around 35% during the reboot and then rolling back with error 0x800f0922.

The cause was oddly specific. It wasn't your disk being full; it was the EFI System Partition, a hidden ~100 MB area that holds the files Windows needs to boot. On PCs where firmware updates or past reinstalls had nibbled away at it (leaving under about 10 MB), the update had nowhere to write and gave up. A smaller group also reported slower internet and a Windows Hello glitch afterward.

What to do: Microsoft shipped a fix on May 26 (KB5089573), so the simplest cure is to install the latest update and reboot - it clears the failure for most people. Don't switch off security updates to make the error disappear; the May patch closed real holes.

A patch that won't take is exactly the kind of thing worth double-checking. Tendvane's Windows Update panel shows whether your updates actually installed, and its Repair tab has a one-click "Windows Update is stuck" fix that clears the update cache when a monthly build refuses to go on.