Sen's (1970) theorem on the impossibility of a Paretian liberal depends on the presence of externalities. Saari and Petron (2006) show that for any Sen cycle, every decisive individual suffers at least one strong negative externality. We show that this result only holds when individual preferences are strict. We prove a general theorem for the case of weak preferences. (C) 2016 Elsevier B.V. All rights reserved.