Work-family conflict (WFC) is a common experience which frequently affects employees’ job performance. But among dual-earner couples, is it possible that the effects of WFC jump from the employee to the spouse, affecting spouses’ job performance? And what is the reason why this happens? Drawing on crossover literature and cognitive activation theory, we propose that when employees experience WFC, their spouses will not be able to detach from home-related issues on the next day (particularly if they experience negative activation), and that is the reason why they will not perform well at work. Moreover, we propose that low performance will affect the ability to detach from work during the evening. We conducted a diary study among 145 working couples who responded to a daily survey over five consecutive working days. Our results largely support our hypotheses. Employees’ WFC leads to lower spouses’ performance on the following day via lower spouses’ home detachment. In addition, home and work detachment are directly related and indirectly related via job performance. We show that WFC has an effect on spouses beyond the family domain, and that detachment from family-related issues is key not only to performing well but also to disconnecting from work.