Impostor syndrome--feeling like a fraud who does not belong--is commonly reported by postsecondary students. Using a cross-sectional survey, we found that heightened imposturous feelings were reported by students of subjectively lower socioeconomic status (SES), and that this association was explained by lower university engagement. Further, if a greater proportion of a participant's friends were cross-SES friends, the relationship between lower subjective SES and imposturous feelings was stronger. This demonstrates a downside to cross-group friendships and generates directions for future research and interventions.