National identities are often conceived of as factors that lend structure and stability to citizens’ political opinions on issues such as immigration: While citizens who define national membership in ethno-cultural terms are less likely to support immigration, those with a civic conception are more likely to do so. We propose that defining national identity along both ethno-cultural and civic lines may give rise to conflicting considerations leading people to experience ambivalence, implying that national identities may serve less as a stabilising force than suggested by previous research. Findings from heterogeneous choice models and a unique survey experiment show that German citizens with mixed conceptions of national identity had more variable and more malleable opinions than individuals with ideal-type conceptions during the 2015/2016 European refugee crisis. Our findings point to an identity-based source of ambivalence and extend our knowledge of how people form attitudes towards immigration.