Windows 11 May Update Stuck at 35%? Here’s the Fix

If your Windows 11 machines have been stalling on the May 2026 security update (KB5089549) and rolling back with an error, you’re not alone. Microsoft has confirmed the issue: a small hidden partition that Windows uses to start up has run out of breathing room, and the update can’t complete without it.

This isn’t a disaster. The machine keeps working fine for day-to-day tasks. But it does mean your devices are missing this month’s security patches, which cover a number of known vulnerabilities. That’s not something to leave sitting.

What’s Actually Going On

Every Windows PC has a small, normally invisible partition called the EFI System Partition. Think of it as the shelf your PC uses to find its own feet when you power it on. It’s hidden because you’re not supposed to need to touch it. Over time, as Windows installs updates and manufacturers add their own boot files, this shelf slowly fills up.

KB5089549 is a routine monthly security update released on 12 May. To install it, Windows needs to write new boot files to that partition. If there’s less than 10 MB free, which sounds like plenty until you realise the whole partition is typically only around 100 MB to start with, the update fails and rolls back at around 35% with error code 0x800f0922. Tech Republic has a good write-up on the issue if you want the full detail.

Missing monthly security patches is worth keeping an eye on. As we covered in why the UK’s cyber threat is climbing, keeping software updated is one of the five controls that blocks the vast majority of common attacks.

What to Do About It

Microsoft has already pushed out a cloud-based fix that’s rolling out automatically to home and unmanaged devices. If you restart your PC and try the update again, it may now go through without any fuss. Worth trying first.

If it’s still failing, there are two options:

• Quick workaround: Open Command Prompt as administrator and run reg add “HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc” /v EspPaddingPercent /t REG_DWORD /d 0 /f, then restart and try the update again. This tells Windows to use a bit less reserved space during the install, which is usually enough to get it through.
• Proper fix: Physically resize the EFI partition using partition-management software so this doesn’t keep happening. It’s not dangerous when done carefully, but it does need a bit of technical confidence and a solid backup in place before you start. Microsoft is working on a permanent fix expected with the June 2026 update. If you’ve got several machines affected, though, waiting a month with unpatched devices isn’t ideal.

Get the patch installed and your machines are back where they should be. Dragon Digital handles Windows update issues for businesses across North Wales, so if you’re not sure whether your machines are affected or you’d rather not poke around in the registry yourself, we can sort it quickly.