Chris Hom argued that slurs and pejoratives semantically express complex negative prescriptive properties, which are determined in virtue of standing in external causal relations to social ideologies and practices. He called this view Combinatorial Externalism. Additionally, he argued that Combinatorial Externalism entailed that slurs and pejoratives have null extensions. In this paper, I raise an objection that has not been raised in the literature so far. I argue that semantic theories like Hom’s are forced to choose between two alternatives: either they endorse an externalist semantics that determines prescriptive properties, or they endorse the null extensionality thesis, but they can’t have both.