Backup external drive files to OneDrive

Hi I need to back up files held on an external drive. This used to be possible with OneDrive, but now it seems that only files resident on the C: drive can be synchronized to OneDrive. That will not work for me; my C: drive isn't large enough to accommodate all the files I need to back up. Is there a way to backup files from drives other than the C: drive, or was that capability removed for good? Thanks,