Microsoft Confirms Windows 11 May Update KB5089549 Fails With Error 0x800f0922 on Devices With Limited EFI Partition Space

Microsoft has confirmed that the Windows 11 May 2026 Security Update KB5089549, released on May 12, is failing to install on some devices running versions 24H2 and 25H2. The installation often fails during the reboot process, usually around 35 percent, and displays error code 0x800f0922. In affected systems, the update rolls back and shows a message indicating that changes are being undone.

The main cause appears to be limited free space in the EFI System Partition. Devices with 10MB or less available space are most likely to experience this issue.

What Windows 11 KB5089549 Installation Failures Look Like

In addition to the rollback message, affected systems might display related entries in C:\Windows\Logs\CBS\CBS.log that point to insufficient free space on the EFI System Partition. Examples of these log entries include:

• SpaceCheck: Insufficient free space
• ServicingBootFiles failed. Error = 0x70
• SpaceCheck: used by third-party or OEM files outside of Microsoft's boot directories

These messages indicate that the issue is related to space rather than a broader problem with the installation process.

Microsoft’s Known Issue Rollback Mitigation And Workaround for Persistent Errors

e has implemented a mitigation using Known Issue Rollback (KIR) for consumer and unmanaged business devices. In many cases, simply restarting the computer and checking for updates again will allow the update to install normally without any additional steps.

For devices managed by an organization, network administrators need to manually deploy a Group Policy workaround to apply the mitigation.

For systems that continue to experience issues after applying the KIR mitigation, Microsoft has provided a registry workaround. This reduces the reserved padding that Windows uses inside the EFI partition during servicing.

Editing the registry can be risky and may cause damage to the system if done incorrectly. It is advisable to back up the entire system before making any changes.

To implement the workaround, open the Start menu, search for Command Prompt, right-click on the top result, and select Run as administrator.

1. Type the given command and press Enter. After that, restart the computer.
2. Next, open Settings and navigate to Windows Update.
3. Click on Check for updates. The update

KB5089549 should now download and install successfully after the registry change has been applied.

Permanent Fix in Development and Other 2026 Windows 11 Update Issues

Microsoft has announced it is working on a permanent fix for the issue, which will be included in a future Windows update. No specific timeline has been given for when the fix will be released.

This problem is the latest in a series of issues affecting Windows 11 updates in 2026. The April update caused third-party backup software to break due to a vulnerable driver block, and in the same month, Windows Server 2025 systems experienced BitLocker recovery prompts and failures during update installations.

Devices with older hardware or upgraded system configurations tend to be more affected by these partition and servicing issues.

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