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?