This article offers an argument of genocide denial as an injustice perpetrated not only against direct victims and survivors of genocide, but also against future members of the victim group. In particular, I argue that in cases of persistent and systematic denial, i.e. denialism, it perpetrates an epistemic injustice against them: testimonial oppression. First, I offer an account of testimonial oppression and introduce Kristie Dotson’s notion of testimonial smothering as one form of testimonial oppression, a mechanism of coerced silencing particularly pertinent to genocide denialism. Secondly, I turn to the epistemology of genocide denialism and, using the example of Turkey’s denialism of the Armenian genocide, show how it presents what Linda Martín Alcoff calls a substantive practice of ignorance. Thirdly, I apply these considerations to individual practices of genocide denial and analyse the particular characteristics of testimony on genocide, the speaker vulnerabilities involved and the conditions under which hearers will reliably fail to meet the dependencies of a speaker testifying to genocide. Finally, I explore the harms that testimonial oppression perpetrates on members of the victim group, insofar as it systematically deprives them of epistemic recognition.