Convert Windows boot from BIOS to UEFI without decrypting Bitlocker

I wanted to convert an MBR/BIOS boot drive to GPT/UEFI, but without needing to decrypt and then re-encrypt Bitlocker. Mainly because I am lazy. This worked, but I’ll warn that the advice to decrypt completely first is without any doubt the safest way to go.

Follow the instructions for converting from BIOS to UEFI boot.

With the following changes:

  • Print out your Bitlocker Recovery Key from Control Panel, Bitlocker. You will need this key.
  • Take a backup. No seriously. Use Veeam Endpoint if you don’t have anything else installed to take backups. Stuff goes wrong with computers, and you don’t want to lose your system installation and data.
  • Suspend Bitlocker protection on your system drive.
  • Reboot from your Windows installation / recovery DVD/USB, verify that you can get to your c:\windows directory. This might be d:\windows if you have a recovery partition at the end of the disk.
  • Now boot into Windows and convert to GPT using gptgen
  • When you then boot into the Windows installation / recovery media, you’ll be asked for the Bitlocker Recovery Key. After that, the rest of the steps are as in the generic instructions.
  • When booting into Windows (assuming you changed your BIOS to boot (U)EFI instead of MBR now), you’ll be asked for the recovery key again.
  • In my case, the drive didn’t show suspended. I suspended it again.
  • After that, resuming Bitlocker encryption will fail with “The System cannot find the file specified”.
  • Open Explorer, navigate to C:\Windows\System32\Recovery and rename the file “ReAgent.xml” to “ReAgent.xml.old”
  • Resume Bitlocker encryption on drive C:\ This should now succeed.
  • Reboot for good measure to verify that everything works and you don’t get prompted for the recovery key any more.
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