Leftist and rightist populist parties in Western Europe both oppose trade openness. Is support for economic protectionism also relevant for their electorates? We assess this in the Netherlands, where both types of populist parties have seats in parliament. Analyses of representative survey data ( n = 1,296) demonstrate that support for protectionism drives voting for such parties, as do the well-established determinants of political distrust (both populist constituencies), economic egalitarianism (leftist populist constituency) and ethnocentrism (rightist populist constituency). Surprisingly, support for protectionism does not mediate the relationship between economic egalitarianism and voting for left-wing populists, or the link between political distrust and voting for either left-wing or right-wing populist parties. In contrast, support for protectionism partly mediates the association between ethnocentrism and voting for right-wing populists. We discuss the largely independent role of protectionism in populist voting in relation to the cultural cleavage in politics and electoral competition, and also provide suggestions for future research.