Microsoft has confirmed a new issue affecting the May 2026 security update for Windows 11. After installing update KB5089549, some users are seeing installation failures during the restart phase, followed by automatic rollback attempts and the error code 0x800f0922.
The problem appears to impact devices with very limited free space on the EFI System Partition (ESP), particularly systems with 10 MB or less remaining.
Microsoft had released Windows 11 May 2026 Update (KB5089549) with Xbox Mode, File Explorer Improvements & More. You can read more the about it here.
Windows 11 KB5089549 Installation Fails at 35–36%
According to Microsoft, affected devices typically behave like this during installation:
- The update downloads and begins installing normally
- Installation proceeds successfully through the initial phases
- During restart, the process fails around 35–36%
- Windows rolls back the update automatically
- Users may see the message:
“Something didn’t go as planned. Undoing changes.”
The update then fails with the error:
- 0x800f0922
This issue specifically affects the May 2026 security update KB5089549 for Windows 11 version 24H2 and 25H2 systems.
What Causes Error 0x800f0922?
Microsoft says the failure occurs when the EFI System Partition does not have enough available space.
The company identified log entries in:
C:\Windows\Logs\CBS\CBS.log
that point to insufficient EFI partition storage.
Affected logs may contain messages such as:
SpaceCheck: Insufficient free spaceServicingBootFiles failed. Error = 0x70SpaceCheck: <value> used by third-party/OEM files outside of Microsoft boot directories
This suggests that third-party or OEM boot files may also be consuming valuable space inside the EFI partition.
Microsoft Provides Temporary Workarounds
Microsoft has already shared two temporary fixes for affected users while a permanent solution is being developed.
Option 1: Modify the EFI Registry Setting
Microsoft says users can allow the update to install by changing a registry value related to EFI partition padding.
Important:
Editing the Windows Registry incorrectly can cause serious system issues. Users should back up the registry before making changes.
Steps to apply the workaround:
- Open Command Prompt as Administrator
- Run the following command:
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc" /v EspPaddingPercent /t REG_DWORD /d 0 /f- Restart the PC
- Retry installing the update
This workaround reduces reserved padding requirements for the EFI System Partition and may allow the update to complete successfully.
Option 2: Known Issue Rollback (KIR)
Microsoft has also deployed a Known Issue Rollback (KIR) mitigation.
For:
- Consumer devices
- Non-managed business PCs
the fix should apply automatically over time. Restarting the system may help the mitigation deploy faster.
Enterprise & Managed PC Fix
For enterprise-managed systems, IT administrators must manually apply a Group Policy mitigation.
Microsoft says admins can find the required policy under:
- Computer Configuration
- Administrative Templates
- KB5089549 Known Issue Rollback policy
The mitigation temporarily disables the problematic change causing the update failure.
Affected enterprise devices must also be restarted after applying the Group Policy.
Permanent Fix Is Coming Later
Microsoft says a full resolution is currently in development and will arrive in a future Windows update.
Until then, users experiencing installation failures with KB5089549 may need to use one of the provided workarounds to successfully install the May 2026 security update.
The company also noted that it will update its documentation once the permanent fix becomes available.
Why This Matters
Windows update failures involving the EFI System Partition have become increasingly common as modern security updates continue modifying boot-related components.
The issue is particularly frustrating because:
- The update appears to install normally at first
- Failure only happens during reboot
- Windows silently rolls back changes afterward
For users with older OEM systems or heavily customized boot partitions, this bug may become more widespread until Microsoft ships a permanent patch.
New Windows 11 Features and Improvements coming next
Microsoft has finally released “move the taskbar to the top” option to Windows 11 in an insider build. In another major upgrade, Window 11 Start Menu has received features users have been requesting for years like new layout controls, privacy features, size options, and cleaner recommendations.
Microsoft has also added a new CPU boost feature with low latency profiles for improved user experience and improvements like “Infinite Scrolling” and More to Touchpads”. You can read about new features and improvements coming to Windows 11 Start Menu, Taskbar, and Task Manager (NPU AI tracking), refreshed run dialog in our latest coverage.
Microsoft has also delivered Major File Explorer, System Performance, and Update Improvements recently. Stay tuned to WinCentral for all latest news about Windows 11 and keep reading our full coverage here.
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