The democratic peace - the regularity that democracies rarely (if ever) fight with other democracies but do fight with nondemocracies - is one of the most famous findings in international relations scholarship. There is little agreement, however, about the mechanism that underpins the democratic peace. Recently, scholars have shown that mass publics in liberal democracies are less supportive of using military force against other democracies. This finding has been taken to support the idea that the content of public opinion may provide one mechanism that underpins the democratic peace. Using a large-scale survey experiment, we show that mass publics in an authoritarian regime - China - show the same reluctance to use force against democracies as is found in western democracies. Our findings expand the empirical scope of the claim that mass publics are reluctant to use force against democracies, but force us to rethink how public opinion operates as a causal mechanism underpinning the democratic peace.