Microsoft has confirmed a new known issue affecting Windows Server 2016 systems that causes domain controller lookups to fail after installing the KB5087537 May 2026 security update.
Windows Server 2016 reached the end of mainstream support in January 2022, but Microsoft has pushed back the extended support end date by 5 years to allow customers to migrate to newer Windows Server versions.
As the company explained in an updated support document, this affects only devices with hostnames exactly 15 characters long.
"After installing this update, domain controller discovery might fail on Windows Server 2016 systems when the server hostname is 15 characters long," Microsoft said.
"When the hostname is 15 characters long, DCLocator calls (for example, using nltest /dsgetdc:<domain> /pdc) will return ERROR_INVALID_PARAMETER, preventing applications and administrative tools from locating a domain controller."
