Research guided by demographic transition theory has shown that exposure to mortality influences women's fertility preferences and behaviours. Despite the myriad contexts, methodological approaches, and linkages featured in past studies, they have shared a focus on women, leaving questions on the gendered salience of mortality exposures for adults' fertility-related outcomes unanswered. In this research note, we analyse data from three African countries with distinct fertility profiles (Nigeria, Zambia, and Zimbabwe) to examine associations between sibling mortality exposure and ideal family size among women, men, and couples. We also investigate the stability of these associations over time. The associations between adults' sibling mortality exposure and their own and their spouses' ideal family sizes vary across countries. However, the gendered nature of the results in every country and evidence of cross-spousal effects uniformly demonstrate the need to incorporate sex differences into the study of the mortality-fertility link.