Is this an invalid action value in a HTML form?

I have a HTML form which has the following line:

<form action="/?s=test+keywords" method="get">

As you can see, I'm sending the form to the URI "/?s=test+keywords".

I know this is a bit weird, but is this an invalid URI or in theory should this work fine?

Currently it's not working for me (the page which loads is "/?"), but I'm having trouble figuring out why. (I'm using Wordpress, so it's possible Wordpress is rewriting this URI.)

Thanks for your help.