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Windows

Windows Update fails at 35 percent with error 0x800f0922 and undoes the changes

A Windows 11 update gets most of the way through, then rolls back at about 35 percent with 'Something didn't go as planned. Undoing changes' and error 0x800f0922. Microsoft traced one widespread case to a nearly full EFI System Partition, and published both an automatic mitigation and a registry command that lets the update through.

Affects

Versions

  • Windows 11, version 24H2
  • Windows 11, version 25H2

Builds and updates

  • KB5089549
  • OS Build 26100.8457

Hardware

  • PCs whose EFI System Partition has 10 MB or less free space

What you see

  • Windows Update fails with error code 0x800f0922
  • The installation fails during the reboot phase at about 35 to 36 percent complete
  • The screen shows "Something didn't go as planned. Undoing changes"
  • C:\Windows\Logs\CBS\CBS.log contains "SpaceCheck: Insufficient free space" and "ServicingBootFiles failed. Error = 0x70"
  • The PC still reports plenty of free space on the C drive

Why it happens

Confirmed The update needs room in the EFI System Partition, a small hidden partition that holds boot files. Microsoft says the failures happen on devices with "limited free space on the EFI System Partition", especially 10 MB or less. [1] [2] [3]

Likely Windows Central notes that third party and OEM files stored outside the Microsoft boot directories can be what filled the partition, which is why the C drive can look empty while the update still fails. [1] [2]

When it shows up

A home or unmanaged PC where Microsoft's automatic mitigation can arrive

You are in this case if:

  • Settings > Windows Update says updates are not managed by your organization
  • The update failed with 0x800f0922 during the restart phase
  • You have not tried a restart plus a fresh check for updates since the failure

2 fixes below

The update keeps failing with 0x800f0922 after a restart and a fresh check

You are in this case if:

  • The same failure repeats at about 35 percent on every attempt
  • CBS.log shows 'SpaceCheck: Insufficient free space'
  • The device is managed by an organization, or the mitigation has not reached it

2 fixes below

The steps that killed it

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Keeping it away

  • When an update rolls back, read C:\Windows\Logs\CBS\CBS.log before changing anything, because the log names the resource that ran out.
  • Leave the EFI System Partition alone. Third party tools that write into it are what fill the space Windows needs during servicing.

Sources

  1. Resolved issues in Windows 11, version 24H2
    Microsoft Learn, 2026-05-26
  2. Microsoft confirms Windows 11's May 2026 update is failing to install with error 0x800f0922 and outlines a mitigation for affected PCs
    Windows Central, 2026-05-20
  3. Microsoft fixes May update failing to install on some Windows 11 PCs
    PCWorld, 2026-05-19
  4. How to back up and restore the registry in Windows
    Microsoft Support

First seen 2026-05-15 · Vendor status fixed · Fixed in KB5089573, released May 26, 2026 · Last verified 2026-09-14