It is well established that the tonal system of Yoruba involves the asymmetric marking or retention of certain tones and the absence or loss of others. The behaviour of Yoruba's three tones is scalar but non-linear, with H tones being the most stable and M tones being the most unstable. In this note, it is shown that previous accounts of the asymmetries in terms of underspecification are problematic, arguing instead for the incorporation of tonal markedness directly into the formulation of faithfulness constraints.