#+Latex_header not being copied to rst file

[algebravic]

Since I have a lot of latex in my org files, I routinely have lines at the beginning like

#+latex_header: \newcommand{\BB}{\mathbb{B}}

These definitions are necessary for the TeX to be formatted properly. They aren't however being copied into the generated rst file. I have org-version 9.0.5 in emacs 26.3 and ox-rst-20191013.551