How do parties in multiethnic societies shape voter attitudes toward female candidates? We address this question, focusing on parties with ideologies that contain ethnonationalist gender norms—patriarchal norms applied to women from an ethnonationalist party's core ethnic constituency. We argue that, while these norms appeal to an ethnonationalist party's base, they also provide informational cues to the party's “non‐core” voters that undermine their support for the party's “core” female candidates. Evidence from an original conjoint survey experiment in the Indian state of Bihar supports our argument; upper‐caste female candidates suffer a support penalty when they are affiliated with the national ruling party, whose ideology prescribes ethnonationalist gender norms targeting its core Hindu upper‐caste constituency. This penalty, we show, is driven by the party's non‐core voters. Our results, which we further bolster using real‐world electoral data, illuminate when and how ethnonationalist gender norms disadvantage elite female candidates.