One of the central dimensions of traditional masculinity is men's renunciation of the feminine (i.e., the anti-femininity norm), and men's endorsement of this norm constitutes one of the strongest predictors of negative attitudes toward homosexuality. However, egalitarian societies are undergoing a significant change: Gendered roles, stereotypes, and norms are evolving. Accordingly, many believe that men are becoming more feminine than before, and this change might have consequential effects. Across two studies conducted in Western countries, we investigated heterosexual men's reaction to the perceived decline of the antifemininity norm of masculinity on their attitudes toward homosexuality. The results consistently showed that perceived men's feminization increased negative attitudes toward homosexuality (Study 1, n = 220), specifically among those participants who most strongly endorsed the anti-femininity norm (Study 2, n = 156). Furthermore, this pattern was driven by participants' discomfort with homosexuality rather than by their motivation to reinstate the challenged gender dichotomy. We discuss the relevance of these findings for both the gender and sexual prejudice literatures. Keywords Masculinity . Gender roles . Gender norms . Anti-gay prejudice . Heterosexuality . Ingroup distinctiveness One of the central dimensions of traditional masculinity is men's renunciation of the feminine (the anti-femininity norm; e.g., Kimmel 2012;Plummer 2005). Indeed, there is a consistent body of research showing that men often affirm their masculinity by avoiding traditional and stereotyped feminine traits, roles, and behaviors (Bosson and Michniewicz 2013;Branon 1976;Thompson and Pleck 1986). Men's endorsement of the anti-femininity norm also constitutes one of the strongest predictors of negative attitudes toward homosexuality, in particular prejudice toward gay men (Wilkinson 2004).