In 1586, Robert Bellarmine was appointed consultor to the Congregation of the Index of Forbidden Books. In this role, he was asked to consider the relationship between the Tridentine Index (1564) and the recently promulgated bull Coeli et terrae. Prepared under the auspices of Sixtus V, the bull endorsed key aspects of the Thomist approach to astrology outlined in the 1564 Index. It banned, however, making uncertain predictions about future human actions, which Aquinas had allowed. Historians have suggested that the provisions of Sixtus V’s bull were unprecedented and idiosyncratic. In this paper, I challenge these arguments by analysing a series of lectures presented by Robert Bellarmine on Aquinas’s Summa theologica in the 1570s. Whilst Bellarmine accepted the broad thrust of Aquinas’s thought on astrology, he specifically rejected the prediction of future human actions. He continued to support similar views when he commented on the bull and the Index.