The Court of Arbitration for Sport recently upheld a regulation by the International Association of Athletics Federations (IAAF) according to which female athletes with hyperandrogenism should not be able to participate in some women’s competitions unless they reduce their testosterone level by medical treatment. This sex testing policy is frequently used in sport contests, mostly enforced on “suspicious looking women” via methods such as hormonal or chromosomal testing. Based on case law and sport regulations, I show that sport institutions play a major role in reinforcing the dogma of gendered binarity. Mandating “feminity tests” presupposes that every athlete can be assigned to a female or male sex category, making intersex bodies as a nonsense. The result is the production of bodies that are normalized according to gender binary stereotypes. This legal regime is currently contested by athletes (e.g., Caster Semenya) as grounded on sexist and even racist grounds.