Messed up visudo - can't edit the file anymore

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http://askubuntu.com – I really did some very stupid stuff. I did a sudo visudo and wanted to add the following line: %admin ALL = NOPASSWD: /bin/tar so users can execute /bin/tar without the need to sudo. But stupid me replaced the line %admin ALL = (ALL)ALL So basically that means I'm totally locked out. Everytime I try a sudo visudo I get "Sorry, user admin is not allowed to execute '/usr/sbin/visudo' as root on myhost" I only can tar. Great. Is there any way to get my root rights back? (HowTos)