Wiki Server restricting simultaneous page edits

How do I restrict users from simultaneously editing the same Wiki page?

I had a situation today where one person was editing a Wiki page, and a second person started to edit the same page while the first person was still editing. The second person saved their changes. Then the first person went to save and got the message, that another person had edited, and if they save it would overwrite the other person's edit.

It's basically a 'page checkout' question - which doesn't appear to exist in OS X server Wiki

thanks!