Windows 11 May 2026 Security Update Fails on Low Boot Partition Space
The May 2026 Windows update fails on low EFI System Partition space, triggering rollback errors on affected devices.
Key Takeaways:
- Some Windows 11 devices are failing to install the May 2026 security update.
- A hidden EFI partition storage issue is triggering rollback errors.
- Microsoft has issued temporary fixes while criticism over update reliability grows.
Microsoft has confirmed that its May 2026 Windows 11 security update (KB5089549) may fail to install on some systems, triggering an error and rolling back changes during the process. The issue stems from the EFI System Partition (ESP) when it has 10 MB or less of free space available.
The EFI System Partition (ESP) is a small, dedicated section of a computer’s storage drive used by systems with UEFI firmware to start the operating system. It contains essential boot files, such as bootloaders and configuration data, which tell the system how to load Windows or other operating systems during startup. The ESP is typically hidden from regular users, automatically managed by the system, and usually only a few hundred megabytes in size.
According to Microsoft, the update may fail with error code 0x800f0922 on Windows 11 devices if the ESP has 10 MB or less of free space. This problem mainly affects devices running Windows 11 versions 24H2 and 25H2.
“After installing the May 2026 Windows security update (), some devices might experience installation failures with error code 0x800f0922. This issue affects devices with limited free space on the EFI System Partition (ESP), especially when the device has 10 MB or less space available. On affected devices, the installation might proceed through the initial phases but fail during the reboot phase at approximately 35–36% completion. The installation then rolls back with error code, and users might see the message: “Something didn’t go as planned. Undoing changes,” Microsoft explained.
Although it has installation issues, the KB5089549 update remains very important because it fixes a large number of security weaknesses in Windows 11, including dozens of critical vulnerabilities (CVEs) that could allow attackers to exploit systems if left unpatched. These flaws generally relate to areas such as system privileges, remote code execution, and other core components.
Microsoft issues fixes for Windows 11 users
Microsoft has recommended a couple of ways to address this issue, including making a specific registry edit or using a Known Issue Rollback (KIR) to fix the problem. The company mentioned that a fix has already been automatically rolled out to most consumer and unmanaged devices.
The problem surfaced soon after Microsoft highlighted efforts to improve the quality and reliability of Windows updates, which makes the situation particularly ironic. This timing led to criticism from users and IT administrators, who pointed out that recurring update issues continue to undermine confidence in the platform, despite the company’s assurances that quality is getting better.
Rabia has a master's degree in Software Engineering and she has years of experience writing professionally about Microsoft products and other technologies. Rabia has also written for OnMSFT.com as well as Windows Report. She is always up to date on t...
