This chapter situates Kant’s rejection of Stoic eudaimonism within his overarching anti-eudaimonist agenda. The chapter begins by emphasizing the importance of the Stoic tradition for Kant’s critical reception of ancient ethical theory. It then reconstructs the central commitments of ancient Stoic eudaimonism and of Christian Garve’s quasi-Stoic eudaimonism. Turning to Kant’s anti-Stoic argument in the Dialectic of the Second Critique, the chapter argues that the primary target of Kant’s error of subreption (vitium subreptionis) is the Stoic Seneca, specifically his account of joy (gaudium) as an accompaniment of one’s consciousness of virtuous activity. After reconstructing Kant’s argument in detail, the chapter offers a new way to understand its anti-eudaimonist implications: practical illusion leads the Stoic to rationalize and, ultimately, to disfigure the moral law. Even in their moral ardor – or, rather, propelled by it – the Stoic commits an error of self-love.