The inclusion of a labour/leisure choice in endogenous growth models has interesting and somewhat counter-intuitive effects. In existing one sector models, a condition for indeterminacy is that labour demand is upward-sloping, which is difficult to reconcile with the evidence. In this paper we give conditions for indeterminacy in a one sector model with decreasing returns to labour. We show that this requires that consumption and leisure are both highly intertemporally substitutable while the factors of production are highly complementary.