preconv generates a good unicode escape but groff can't find special character

[Filip Banák]

Hi.

First of all, I swear it worked this morning. Then suddenly I process my
.mom file and the 'č' character is gone.

This is the command and output:
preconv file.mom | pdfmom > file.pdf
troff: tema.mom:11: warning: can't find special character 'u0063_030C'

I checked the output of preconv and it definitely outputs the right unicode
codepoint \[u010D].
In LibreOffice Writer, if I select the GNU FreeSans font that I use with
the mom document and insert that unicode codepoint everything shows as
expected.

I am running Arch linux, groff 1.22.4.

I started learning groff a few days ago and now I can't continue, though I
would love to.
Thank You for any help.