In From Chance to Choice, Allen Buchanan, Dan Brock, Norman Daniels and Daniel Wikler propose a new way of defending the moral significance of the distinction between genetic treatments and enhancements. They develop what they call a ‘normal function model’ of equality of opportunity and argue that it offers a ‘limited’ defence of this distinction. In this article, I critically assess their model and the support it (allegedly) provides for the treatment-enhancement distinction. First, I argue that there is a troubling tension in the normal function model. Secondly, I argue that neither of the rationales invoked by Buchanan et al. really serves to justify this model or the results they seek to derive from it with respect to the significance of the distinction between treatments and enhancements.