ABSTRACT Electoral shocks have spillover effects in democracies, as they can change citizens’ political attitudes and political behaviour across national borders. Yet, electoral shocks also exist in non-democratic regimes. Do electoral shocks likewise lead to spillover within a non-democratic regime? To explore this question, I build on Lohmann’s idea of information cascade and study the spillover of the 2019 Hong Kong local election, in which the opposition won a landslide victory. Using a survey fielded in Macau during this event, I find liberalizing effects among middle-class citizens: after the electoral shock, their democratic commitment increases while their perceived electoral fairness decreases. Conversely, lower-class citizens experience backlash effects as they assess the electoral system more positively and briefly consider democracy as less important. However, these changes in political attitudes do not translate into changes in expressed vote choice and other types of political participation. Regarding the mechanism of the attitudinal change, I suggest such polarized reactions are related to the different information consumption among the two classes. I discuss how these findings contribute to the literature on non-democratic regimes, electoral shocks, and class politics.