Fix the EFI Partition Error 0x800F0922 in Windows 11 Today

• Software Engineer Intern
• 28 Sep 2026

Fix the EFI Partition Error 0x800F0922 in Windows 11 Today

Windows 11 error 0x800F0922 tends to hit at the worst moment. The update downloads fine, your PC restarts, the progress bar reaches roughly 35 percent, and then everything rolls back. Here’s what’s actually causing that, and how to fix it, starting with the quickest options and ending with the ones that need a backup first.

Here’s the short version: a small hidden partition is almost full. Your main drive can have hundreds of gigabytes free, and the update will still fail, which is exactly why this error confuses so many people.

What Error 0x800F0922 Means on Windows 11

Microsoft confirmed that the May 2026 security update, KB5089549, failed to install on some Windows 11 24H2 and 25H2 devices with this code, and the failure came during the restart phase at around 35 percent. The system then rolls the update back automatically, leaving the device unpatched.

The trigger was limited free space on the EFI System Partition. PCs with 10 MB or less free were the most likely to fail.

So what is the EFI System Partition, or ESP? It’s a hidden, FAT32-formatted partition that holds the Windows Boot Manager, and your PC can’t start Windows without it. Updates that touch boot files need room to write there. When that room isn’t available, servicing stops.

Why the EFI System Partition Runs Out of Space

Windows itself doesn’t fill this partition quickly. It usually stays under 100 MB total and keeps 60 to 80 percent of that free. But it can grow when OEM updates, such as BIOS updates, add extra files. Microsoft’s own log entries also mention files from third parties or PC makers sitting outside the Microsoft boot folders. Older troubleshooting advice set the bar a little higher, at about 15 MB of free space.

Think of it as a small suitcase: a few vendor files get packed in over the years, and then one day an update needs to add one more item and the zipper won’t close.

Confirm the Cause Before You Change Anything

Guessing wastes time. Two quick checks tell you whether the ESP is really the problem.

Check the log. Open C:\Windows\Logs\CBS\CBS.log in Notepad and search for SpaceCheck and ServicingBootFiles. Messages about insufficient free space, or ServicingBootFiles failing with error 0x70, point straight at the ESP.

Check the free space. Open Command Prompt as administrator and run these three lines:

mountvol S: /S
fsutil volume diskfree S:
mountvol S: /D

The first line mounts the hidden partition as drive S:, the second reports its free bytes, and the third unmounts it again. If the free figure is under about 15 million bytes, you’ve likely found the culprit. If S: is already taken on your PC, pick another unused letter.

Try the easy things first. Microsoft pushed a Known Issue Rollback for consumer and unmanaged devices, and in many cases a plain restart followed by another update check clears the error. If that doesn’t work, Microsoft pointed affected users to the optional preview update KB5089573, and said the permanent fix would ship with the June 9 Patch Tuesday release.

A PC that’s fully up to date by now should already carry that fix. Even so, a nearly full ESP can trigger the same error again on a future update, so it’s worth ruling out regardless of how current your PC is.

Fix 1: Apply Microsoft’s Registry Workaround

Microsoft’s workaround changes a registry value that lowers the padding Windows reserves inside the EFI partition during servicing. You’re editing the registry, so create a restore point or a full backup first. It takes five minutes and can save you a bad afternoon.

1. Right-click Start and open Terminal or Command Prompt as administrator.
2. Run this command:

   reg add "HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc" /v EspPaddingPercent /t REG_DWORD /d 0 /f

3. Restart your PC.
4. Open Settings, choose Windows Update, and click Check for updates.

Windows Central reports that the failing update should then download and install without issues. Microsoft calls this a workaround rather than a permanent fix, and there’s no long-term data yet on leaving the value at 0, so treat it as a stopgap. If the ESP is only slightly short on space, this is the least invasive fix. If it’s badly full, move on to Fix 2.

Fix 2: Free Up Space on the EFI Partition

When the registry tweak isn’t enough, clear room by hand. This is the core fix for a full EFI partition, and it deserves care, because the files in there are what start your PC.

Before you begin, suspend BitLocker if it’s turned on. Changes to boot files can trigger a recovery key prompt.

1. Open Command Prompt as administrator and mount the partition: mountvol S: /S
2. Back up its contents to your main drive: xcopy S:\EFI C:\ESP_Backup /E /H /I /K
3. Look around with dir S:\EFI and dir S:\EFI\Microsoft\Boot\Fonts
4. Delete the boot menu fonts: del /f S:\EFI\Microsoft\Boot\Fonts\*.ttf
5. Recheck the free space with fsutil volume diskfree S:, then unmount with mountvol S: /D
6. Restart and run Windows Update again.

Those fonts only draw text on the boot menu, and Windows generally rebuilds what it needs. Leave bootmgfw.efi and the BCD file alone; delete those and Windows won’t start. If you spot folders from your PC maker or an old Linux install, don’t remove them unless you know what they do. They can hold firmware tools or dual-boot files.

Fix 3: Enlarge the EFI System Partition

If the ESP is tiny and cleanup only buys back a few megabytes, the lasting solution is a bigger partition. Disk Management can’t do this, because the ESP sits at the start of the disk with other partitions beside it. A third-party partition manager can shift things around and extend it. Many guides suggest 260 MB or more, though the right number depends on your disk.

A few ground rules:

• Take a full disk image backup first. A power cut mid-resize can leave a PC unbootable.
• Suspend BitLocker before you start.
• Plug in a laptop; don’t run this on battery.
• Choose a tool with a solid reputation for GPT and UEFI disks.

Fix 1 and Fix 2 are usually enough. If resizing sounds like too much, that’s a fair call, and a technician can handle it.

Other Causes Worth Ruling Out

Not every case like this comes from a full ESP. Older reports point to a disabled App Readiness service, a missing or mislabeled EFI partition, an uninstalled Microsoft Edge, third-party antivirus blocking the install, and damaged performance counters. If the log shows no space problem, work through these:

• App Readiness service: open services.msc, double-click App Readiness, set startup to Manual, and restart.
• Security software: pause third-party antivirus during the install.
• VPN: some people report failures while connected, so disconnect and retry.
• System files: run sfc /scannow, then DISM /Online /Cleanup-Image /RestoreHealth, and restart.

This matches what shows up on Microsoft’s community forums and Reddit threads about the May update: the same failure around 35 percent, and a restart and retry that clears it for a lot of people before they ever touch the registry or the partition.

Mistakes That Make This Worse

• Deleting the wrong files. Anything under EFI\Microsoft\Boot other than the fonts is off limits unless you know exactly what it does.
• Skipping the backup. One xcopy command is cheap insurance.
• Formatting the ESP. Some forum posts suggest wiping it so Windows recreates it. That can leave you with a PC that won’t boot, and it’s a job for proper recovery media.
• Retrying blindly. Every failed attempt means another rollback. Read the log after the first failure instead of trying five times.
• Judging by C: drive space. Plenty of free storage on the main drive says nothing about the hidden partition.

Conclusion

This error usually comes down to one thing: a nearly full EFI System Partition. Start by confirming that in the CBS log, then work up the ladder: restart and retry, install the latest update, apply Microsoft’s registry workaround, clear space by hand, and only then consider resizing the partition. If the log points somewhere else, check the App Readiness service, antivirus, and system file repairs.

Take backups before touching boot files, and don’t delete anything you can’t name. For more help, see our guides on Windows Update troubleshooting and on backing up a Windows 11 PC.