Windows boot partition runs out of space for Microsoft’s May security update

OSes

Testing? We’ve heard of it

Microsoft has admitted that the May 2026 security update might fail to install with a “Something didn’t go as planned. Undoing changes” message.

The problem is related to the EFI System Partition (ESP), which is usually where the device boots from. Its minimum size is 200 MB, and the operating system manages it. However, if there is 10 MB or less free space, then the update might fail with a 0x800f0922 error code and the helpful message.

“On affected devices, the installation might proceed through the initial phases but fail during the reboot phase at approximately 35-36% completion,”  Microsoft said.

As with all security updates, there is important stuff in here that needs to be installed. In our earlier coverage, we called this a “doozy of a Patch Tuesday.” While nothing was reported as being under active attack, there were dozens of fixes for critical Microsoft CVEs.

On devices experiencing the issue, Microsoft has suggested either a registry edit, which will have administrators rolling their eyes, or a Known Issue Rollback (KIR) to deal with the problem. The company wrote: “The resolution has already propagated automatically to consumer devices and non-managed business devices.”

The issue affects Windows 11 25H2 and 24H2, and emerged while Microsoft was enjoying a period of no known issues with its operating system products. The admission was made doubly unfortunate by coinciding with a company blog post titled “Improving Windows Quality”.

Microsoft clearly has more work to do on the quality front, which, frankly, is understandable. Windows is more akin to a supertanker than an agile skiff, and changing direction will take time. However, as administrators reach for the KIR group policy to deal with this latest issue, many would be forgiven for looking at Microsoft’s protestations around quality and muttering the infamous aphorism: “The more things change, the more they stay the same.” ®