Public intervention addressing the issue of underage marriage emphasizes policies such as girls' education and enforcement of age-of-consent laws as promising avenues for ending this harmful practice. It has been argued, however, that such policies will work better in societies where they are supported by men. Yet, there is no study analyzing the role of males' characteristics in relation to early marriage. This paper examines the causal effect of a male's education on the likelihood that he marries an underage girl. Using micro-level data from Nigeria in combination with plausible instrumental variables that address potential endogeneity issues, we find that having more years of schooling significantly reduces the probability of marrying an underage girl. Importantly, we show that this negative relationship is not a mere mechanical effect reflecting the endogeneity between schooling and marriage-timing decisions. Moreover, we find that this relationship is weaker in communities where norms that cast women in submissive roles are stronger. We develop a model that explains this causal effect as resulting from the complementarity between father's and mother's education in the production of child quality.