It is generally assumed that the development of modality proceeds in a unidirectional manner from deontic to epistemic meaning. In this article, we present crosslinguistic data in contradiction of this hypothesis by showing that markers of possibility can, albeit rarely, develop to prohibitives by following a path of semantic change that includes warnings as intermediary links. In addition, this rare development is interesting in that it involves a polarity shift from an affirmative marker to a negative meaning.