How to create a WikiLink to a page in a subdirectory?

I have a page I want to create Wikilink to in 


   website/subdir/page.mdwn


And the wikilink I want to create should be in a page in the website root directory:


   website/index.mdwn


If I just write

    \[[page]]

it seems it will assume the page should be found at


  website/page.mdwn

and adds a question mark ? in front of the link in the generated HTML file. 

How to make such a Wikilink?