- Recent work on consistent Kaluza-Klein reductions on Einstein-Sasaki spaces prompted an intriguing conjecture that there might exist a consistent S 5 reduction of type IIB supergravity to give five-dimensional N = 8 gauged supergravity coupled to a massive supermultiplet that includes the breathing-mode scalar. Motivated by this, we investigate the possibility of augmenting the usual N = 8 supergravity reduction to include a breathing-mode scalar, and we show that this is in fact inconsistent. The standard reduction to the massless N = 8 supermultiplet depends for its consistency on a delicate interplay between properties of the ten-dimensional type IIB theory and properties of the Killing vectors on S5. Our calculations show that turning on the breathing-mode is sufficient to destroy the balance, and hence render the reduction inconsistent. SISSA 2012.