Microsoft’s May 12, 2026 cumulative update for Windows 11, KB5089549, is failing to install on a significant number of PCs, throwing error 0x800f0922 and warning that the EFI System Partition (ESP) lacks sufficient free space. The issue affects both Windows 11 24H2 and the newer 25H2 feature update, leaving systems exposed to unpatched security vulnerabilities until a fix is applied. Microsoft has confirmed the problem and is investigating, but for now, users must manually enlarge their EFI partitions or wait for a tailored solution from the company.

What’s happening?

KB5089549 arrived as part of the May 2026 Patch Tuesday rollout, delivering critical security fixes and quality improvements. During installation, some systems hit a wall: the update fails with error 0x800f0922, and a message indicates there isn’t enough space in the EFI System Partition. The EFI partition is a small, hidden slice of the disk – typically 100 MB to 500 MB – that holds the boot loader, drivers, and system recovery tools. When it runs low on free space, major updates like this one cannot complete.

Several users on the Windows 11 subreddit and Microsoft’s own Tech Community forums began complaining hours after the update’s release. “Stuck at 20% then rolls back,” one commenter wrote. “Never had this issue before, and now I’m unprotected.” The reports quickly spread, revealing that the problem is not isolated to older hardware or specific configurations. Custom-built desktops, laptops from Dell, HP, and Lenovo, and even some virtual machines are affected when the EFI partition has less than roughly 20–30 MB of free space.

Which systems are affected?

The bug hits Windows 11 24H2 and 25H2 installations. Windows 10 and Windows Server are not impacted by this specific failure, though similar EFI-partition-size issues have appeared in past updates like KB5034441. Microsoft has not published an exhaustive list of affected models, but early data suggests that systems with the default Windows-created EFI partition size of 100 MB are most at risk. Machines that shipped from the factory with larger EFI partitions (200–500 MB) or those where users have already expanded the partition are unlikely to see the error.

Dual-boot setups with Linux often have custom EFI partitions that are larger, so they generally bypass the problem. However, systems that have undergone multiple feature update upgrades without cleaning up old recovery files may have a cluttered EFI partition, further shrinking available space.

Understanding the 0x800f0922 error

Error 0x800f0922 is not new to Windows 11. It broadly means “part of the installation failed” and is often tied to insufficient disk space, network timeouts, or corrupted system files. In the context of KB5089549, it specifically points to the EFI partition being unable to accommodate the updated boot files or recovery image that the patch attempts to write. The main culprit is the new Windows Recovery Environment (WinRE) image that the update includes. When the system tries to stage these files inside the EFI partition during the offline installation phase, it finds too little free space and triggers a rollback.

This space check has been present in Windows setup for years, but its enforcement has grown stricter with recent cumulative updates. Microsoft has been steadily increasing the size of WinRE images to include more drivers and remediation tools, especially with the AI-assisted recovery features introduced in 25H2. As a result, the old 100 MB EFI partition – once sufficient – now falls short.

Why EFI partition space matters

The EFI System Partition is a mandatory component of all UEFI-based Windows installations. It is formatted as FAT32 and contains the Windows Boot Manager, boot configuration data, and, if the system uses it, the Windows Recovery Environment files. Because it resides at the very beginning of the disk in most cases, resizing it later is possible but tedious. It’s not something the average user ever thinks about until an update refuses to install.

When the partition is nearly full, Windows Update cannot stage the necessary temporary files. The process that copies and compresses the new WinRE image fails, and the installer backs out. This leaves the system without the new security patches and sometimes with a half-finished update attempt that can cause other stability issues.

Official Microsoft response

On May 13, 2026, Microsoft acknowledged the problem in a support document entry for KB5089549. “After installing this update, you might receive an error 0x800f0922 if the EFI system partition does not have enough free space,” the note reads. “We are working on a resolution and will provide an update in an upcoming release.” The company advises affected users to manually resize their EFI partition or to seek assistance from their PC manufacturer’s support.

There is no timeline yet for a fully automatic fix. It’s unclear whether Microsoft will deliver a separate repair script, adjust the update to require less space, or fold the fix into a subsequent Patch Tuesday. For now, the burden is on the user or IT admin to intervene.

Workaround 1: Manual EFI partition resize using Diskpart

Advanced users can expand the EFI partition by shrinking an adjacent partition, typically the Windows C: drive, and then extending the ESP. Here is a tested method:

  1. Back up your data. Mistakes in disk partitioning can render the system unbootable.
  2. Open an elevated Command Prompt or PowerShell.
  3. Run diskpart.
  4. List disks with list disk, then select the system disk: select disk 0 (replace 0 with your disk number).
  5. List partitions: list partition. Identify your EFI partition (usually the first, labeled “System”, about 100 MB).
  6. Select the Windows partition (usually the largest) with select partition X where X is the number of your C: drive partition.
  7. Shrink the partition to free up space: shrink desired=200. This will create 200 MB of unallocated space immediately after the C: drive.
  8. Now select the EFI partition: select partition Y (Y being the EFI partition number).
  9. Extend it into the unallocated space: extend.

On some systems, you may need to first move recovery partitions or use a third-party tool because the unallocated space must be directly after the EFI partition. If the EFI partition is not at the end of the disk layout (common with OEM partitions in between), this method won’t work without deleting intervening partitions. That’s where a dedicated partition manager comes in.

Workaround 2: Third-party partitioning tools

Software like EaseUS Partition Master, MiniTool Partition Wizard, or the open-source GParted can resize partitions more flexibly. Boot from a live USB of GParted, then:

  • Shrink the main Windows partition to the left to create unallocated space next to the EFI partition.
  • Move any intervening partitions (like the Microsoft Reserved partition or a recovery partition) to consolidate free space.
  • Expand the EFI partition to at least 300 MB.

After resizing, reboot into Windows and rerun Windows Update. The error should be resolved, provided the partition now has enough free space. Many users on forums have confirmed success with this approach, though it requires caution and a recovery plan.

Workaround 3: Clean install with a pre-sized partition

If resizing seems too risky, a clean installation of Windows 11 25H2 with a custom partition layout is the nuclear option. During setup, when you reach the partition screen, delete all existing partitions and create a new one. Windows will automatically create an EFI partition of 100 MB, but you can use Shift+F10 to open Command Prompt and manually create a larger partition with Diskpart:

diskpart
list disk
select disk 0
clean
convert gpt
create partition efi size=300
format quick fs=fat32
assign letter=S
create partition msr size=16
create partition primary
format quick fs=ntfs
assign letter=C
exit

Then proceed with installation. This ensures a 300 MB EFI partition that will satisfy future updates. However, it wipes all data, so backups are essential.

Potential risks and caveats

Resizing system partitions carries real danger. If the EFI partition becomes corrupted, Windows will not boot. Always have a recovery drive or installation media at hand. Also, if you use BitLocker, suspend protection before making any disk changes. Some OEM systems have factory recovery partitions that are referenced in the BCD; moving or deleting them can break factory reset functionality.

Another nuance: the EFI partition must remain FAT32. Extending it with the wrong file system will make it unreadable by UEFI firmware. Stick to tools that preserve formatting. After resizing, you may need to repair the boot loader using bcdboot C:\Windows /s S: (where S is the mounted EFI partition letter) if the system does not boot.

How to check your EFI partition free space

Before panicking, check if you actually need to resize. Open Disk Management (diskmgmt.msc) and look at the small “EFI System Partition” at the start of the disk. If it shows less than 30 MB free, you’re likely in trouble. For a more precise view, use PowerShell:

Get-Partition | Where-Object { $_.Type -eq ‘System’ } | Select-Object Size, @{Name=’FreeMB’; Expression={[math]::Round($_.SizeRemaining/1MB,2)}}

Alternatively, fsutil volume diskfree z: (if you assign a temporary drive letter Z to the partition) gives used and free blocks under the “Total # of free clusters” line.

Timeline for an official fix

Microsoft’s typical cadence for such an issue involves a Known Issue Rollback (KIR) if the problem is server-side configurable, but this is not a policy change. The more likely path is a revised update package that reduces the EFI space requirement, to be released either as an out-of-band update or as part of the June 2026 Patch Tuesday. Until then, the manual workaround remains the only option.

Enterprise IT admins should weigh the urgency of the security patches against the operational risk of resizing partitions on hundreds of endpoints. Deploying the update via WSUS or SCCM can be paused, but that leaves systems vulnerable. Some organizations are opting to first expand EFI partitions using task sequences or scripts while monitoring Microsoft’s release health dashboard for a better fix.

User reactions and community reports

Across the Windows 11 subreddit, several megathreads popped up within 24 hours. Many users expressed frustration that Microsoft did not test for this edge case, given it mirrors the KB5034441 fiasco from 2024. One top comment read, “It’s 2026 and they still can’t figure out how to handle small EFI partitions.” Others shared step-by-step guides, with a popular YouTube tutorial racking up 50,000 views in a day. The Microsoft Tech Community forum also saw an influx of similar reports, with an official engineer periodically asking for diagnostic logs.

Some users noted that the error only appeared when they had certain drivers loaded or after a previous update had partially failed. However, the common denominator remains EFI partition free space. The collective troubleshooting effort underscores the importance of documenting partitioning workarounds for Windows consumers and IT pros alike.

Next steps for affected users

If you see error 0x800f0922 after attempting KB5089549, do not repeatedly retry the update. Each attempt rewrites temp files and can fragment the disk further. Instead, first check your EFI partition space. If it’s below 30 MB free, expand it using one of the methods above, then manually attempt the update again from Settings > Windows Update.

For those uncomfortable with disk tools, waiting for Microsoft’s automated fix might be prudent, but it leaves the system unpatched. Install other non-OS updates normally, and keep an eye on the Windows release health page for updates to KB5089549’s known issues list.

KB5089549’s EFI partition hurdle is yet another reminder that the Windows servicing stack’s appetite for disk space continues to grow beyond the defaults that shipped with PCs just a few years ago. Whether Microsoft delivers a rescaling tool or a refined update payload, the episode highlights the underappreciated importance of proper disk layout in modern Windows installations.