Microsoft has published a support document today warning Windows 10 users that the impending May 2019 Update may not install on their systems if they use external USB storage devices or SD cards.

The OS maker cited problems with "inappropriate drive reassignment" as the main reason for blocking the May 2019 Update.

"Inappropriate drive reassignment can occur on eligible computers that have an external USB device or SD memory card attached during the installation of the May 2019 update," the company said. "For this reason, these computers are currently blocked from receiving the May 2019 Update."

Fortunately, there's a quick and simple workaround for this issue. Microsoft recommends that users remove any external USB or SD media and restart the May 2019 Update installation.

This includes USB thumb drives, USB-based external hard-drives, or SD cards inserted into card reader devices. Unless users are running Windows 10 from one of these devices --which is highly unlikely-- most users will be able to work around this issue.

In the long run, Microsoft plans to address the "inappropriate drive reassignment" issue in a future Windows 10 servicing update.

Microsoft won't block the May 2019 Update for all Windows 10 users, but only those running the April 2018 Update (Windows 10, version 1803) or the October 2018 Update (Windows 10, version 1809). Users using older versions of Windows 10 will be able to move to the May 2019 Update without problems.