Custom search form warning

Hi,

My theme has a custom search form included in the header, similar to the one from the codex.
I need a custom one, because I’m using it for searching through posts only.

When running Theme Check, the following warning is returned:

WARNING: role="search" was found in header.php. Use get_search_form() instead of hard coding forms. Otherwise, the form can not be filtered.

I don’t like warnings, is there a solution for this? Can I fix this somehow?

Guido