Four studies (n = 1199) tested support for the idea that implicit theories about the fixedness versus malleability of gender roles (entity vs. incremental theories) predict differences in the degree of gender system justification, that is, support for the status quo in relations between women and men in society. Relative to an incremental theory, the holding of an entity theory correlated with more system-justifying attitudes and self-perceptions (Study 1) for men and women alike. We also found that strength of identification with one's gender in-group was a stronger predictor of system justification for men than it was for women, suggesting men's defense of the status quo may be motivated by their membership in a high status group in the social hierarchy. In 3 experiments, we then tested whether exposure to a fixed gender role theory would lead men to identify more with masculine characteristics and their male gender group, thus increasing their defense of the gender system as fair and just. We did not expect a fixed gender role theory to trigger these identity-motivated responses in women. Overall, we found that, by increasing the degree of psychological investment in their masculine identity, adopting a fixed gender role theory increased men's rationalization of the gender status quo compared with when gender roles were perceived to be changeable. This suggests that, when men are motivated to align with their masculine identity, they are more likely to endorse the persistence of gender inequality as a way of affirming their status as "real men."