Microsoft’s May security update KB5089549 is failing to install on some Windows 11 machines. Microsoft has now acknowledged on this support page that the installation of this important update fails on some computers—while displaying error code 0x800f0922—if there is insufficient free space on the EFI System Partition (ESP):
After installing the May 2026 Windows security update, some devices might experience installation failures with error code 0x800f0922. This issue affects devices with limited free space on the EFI System Partition, especially when the device has 10 MB or less space available.
In this case, here’s what happens:
On affected devices, the installation might proceed through the initial phases but fail during the reboot phase at approximately 35–36% completion. The installation then rolls back with error code, and users might see the message: “Something didn’t go as planned. Undoing changes.”
Resulting from this issue, users may observe log entries similar to the following in C:\Windows\Logs\CBS\CBS.log, indicating insufficient free space on the EFI System Partition:
- “SpaceCheck: Insufficient free space”
- “ServicingBootFiles failed. Error = 0x70”
- “SpaceCheck: used by third-party/OEM files outside of Microsoft boot directories”
This issue currently affects Windows 11 versions 25H2 and 24H2, but not Windows Server editions.
Microsoft offers two workarounds for affected users.
One option is to use Known Issue Rollback (KIR) to roll back the problematic update to a previous version, restoring the system to its state prior to installing the update. This is the safer option for those who don’t have a lot of experience tinkering with Windows system files.
If you do have experience and admin rights, you can install the update with a registry tweak. Open the Power User menu with the Windows key + X shortcut, launch Terminal as Admin, and enter this command:
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc /v EspPaddingPercent /t REG_DWORD /d 0 /f"
Then restart your PC and try installing the update again.
Microsoft is working on a permanent fix for this issue and will release it as part of one of the upcoming Windows updates.
