Out of the box, Plone's accessibility compliance is outstanding, especially Plone 5. However when building a real site things can go wrong - in the theme, in add-ons, and in customizations. In this talk I'll describe the things that went wrong on a highly customized academic Plone site, which were discovered by an institutional audit. I'll describe the types of errors that were found, how common they were and how difficult to fix. I'll provide guidance on what to look out for when developing a new site. And I'll give my wishlist of Plone accessibility improvements.