For a wide class of infinitely lived agent models, Chamley has shown that the optimal capital income tax rate is zero in the long run. Lucas has argued that for the U.S. economy, there is a significant welfare gain from switching to this policy. This paper shows that for the Bewley class of models with incomplete insurance markets and borrowing constraints, the optimal tax rate on capital income is positive, even in the long run. Therefore, cutting the capital income tax to zero may well lead to welfare losses.