This essay applies Valerie Flint’s thesis about the adoption of astrology and derivative forms of prognostication by the medieval Catholic Church to Catalan treatises on astrology. Two main arguments against the practice of magic in the Middle Ages actually favored the development of astrology and astrological magic. By demonstrating that astrology does not subjugate free will to celestial bodies or contravene God’s authority, Christian astrologers smuggled it into the mainstream of scientific practice. Catalan scholars contributed to this defense, providing textual evidence from the thirteenth to the late fifteenth centuries. The use of these two arguments to defend astrology will become so embedded in the literature that, by the late fifteenth century, such defenses appear as commonplaces. We find them even in popular texts on astrological lore, far removed from their original context as part of academic and theological discourse.