Windows 11 KB5089549 Install Error 0x800f0922 EFI Partition Full

What is KB5089549 Install Error 0x800f0922?

KB5089549 is the Windows 11 cumulative update released on Patch Tuesday, May 13, 2026 for versions 24H2 and 25H2. Error 0x800f0922 during this update almost always traces to the EFI System Partition (ESP) running out of free space. Microsoft confirmed on May 16, 2026 that the new bootloader components in this rollup require at least 10 MB of free space on the ESP, which the Windows partitioning defaults from 2017 and earlier did not always provide.

The install starts, downloads, and reboots into the servicing screen, then rolls back at 35%–36% with the message: *"We couldn't complete the updates. Undoing changes. Don't turn off your computer."* The log entry in C:\Windows\Logs\CBS\CBS.log reads CBS_E_INSTALLERS_FAILED, 0x800F0922.

When does it occur?

• Right after the post-download reboot during KB5089549 installation
• On systems with an ESP smaller than 100 MB (common on PCs imaged before 2018)
• On dual-boot machines where Linux/macOS bootloaders also share the ESP
• After installing a third-party bootloader (rEFInd, Clover, GRUB)
• When the OEM stored recovery agents inside the ESP instead of a separate WinRE partition
• After a previous failed feature update left stale \EFI\Microsoft\Boot\ font and language files

Common causes

• ESP has less than 10 MB free — the hard requirement introduced with the May 2026 servicing stack
• Orphaned bootmgfw.efi.bak and BCD.LOG files from prior cumulative updates
• Stale fonts inside \EFI\Microsoft\Boot\Fonts\ (wgl4_boot.ttf duplicates)
• Third-party EFI bootloader entries consuming partition space
• Recovery agent (Winre.wim) incorrectly stored on the ESP instead of the recovery partition
• Corrupt CBS manifest cache in C:\Windows\servicing\Packages\
• BitLocker pre-boot authentication files left over from a removed configuration

Step-by-step fixes

1. Confirm the error is ESP-related. Open an elevated PowerShell and run Get-WinEvent -LogName Setup | Select-Object -First 30. Look for MoSetup entries citing 0x800f0922 along with SYSTEM partition references.

1. Mount the EFI partition to inspect free space. In an elevated PowerShell:

   mountvol S: /S
   Get-PSDrive S | Select-Object Used,Free

If Free is below 10 MB, this is your root cause.

1. Delete stale font and language files (safe to remove — Windows regenerates them):

   Remove-Item "S:\EFI\Microsoft\Boot\Fonts\*.ttf" -Force
   Remove-Item "S:\EFI\Microsoft\Boot\*.bak" -Force
   Remove-Item "S:\EFI\Microsoft\Boot\BCD.LOG*" -Force

Re-check free space with Get-PSDrive S.

1. Remove orphaned third-party bootloaders if you no longer dual-boot. From elevated PowerShell: bcdedit /enum firmware to list entries, then bcdedit /delete {GUID} for any rEFInd/GRUB/Clover entry you do not use.

1. Apply Microsoft's Known Issue Rollback (KIR) if you cannot free space. On Pro/Enterprise, download the KB5089549-EFISpace-KIR.msi from the Microsoft Update Catalog and import via gpedit.msc -> Computer Configuration -> Administrative Templates -> Microsoft KIR. Home edition users receive the KIR automatically within 72 hours of the May 16 server-side push.

1. Run the in-box update troubleshooter to clear the queued install: Settings -> System -> Troubleshoot -> Other troubleshooters -> Windows Update -> Run. This resets BITS and clears C:\Windows\SoftwareDistribution\Download\.

1. Re-trigger the update from Settings -> Windows Update -> Check for updates. The install should now complete past the 36% reboot point. Verify with winver -> OS Build 26100.4751 (24H2) or 26200.2310 (25H2).

1. As a last resort, resize the ESP. Use a live USB with GParted or the paid MiniTool Partition Wizard to shrink the OS partition by 200 MB and grow the ESP. Back up first — partition resizing can brick the boot configuration. Re-flag the partition as ESP, boot, hidden after resizing.

If it still doesn't work

If the update still rolls back after freeing space, run sfc /scannow followed by DISM /Online /Cleanup-Image /RestoreHealth to repair the component store. A corrupt servicing stack will refuse the install even when the ESP is healthy. If DISM reports an unrecoverable error, perform an in-place upgrade by downloading the latest Windows 11 ISO from Microsoft, mounting it, and running setup.exe — this rebuilds the servicing stack while preserving apps and files. For BitLocker-protected systems, suspend protection before re-running the update (manage-bde -protectors -disable C: -RebootCount 1) to avoid a second recovery key prompt.