It is widely assumed that severe mental disabilities prevent relevant deliberative capacities from developing or persisting. Accordingly, excluding many people with mental disabilities from discourse practices seems justified. Against this common assumption I wish to show that the general exclusion is not justified and amounts to a form of epistemic injustice, as theorised by Miranda Fricker. The received norm of capable deliberators is connected to a specific model of deliberation. I introduce an alternative model of deliberation, which I dub the (...) joint effort model. According to this model, people with minority minds (as I call them) add valuable cognitive diversity to the process of deliberation, which is a relevant element of epistemic improvement. In this part of the argument I rely on empirically informed theoretical work by Hélène Landemore. I scrutinise the minimal requirements of capable deliberators from the perspective of a joint effort model of deliberation, and I highlight specific beneficial contributions people with minority minds can make to discourse practices. I will argue that people with minority minds can be presumptively deemed capable deliberators and that therefore their general exclusion is unjustified. (shrink)