Though approximately one in four coup attempts takes place during an ongoing civil war, scholars have not yet analyzed how the incidence of civil war affects coup attempts and outcomes. We conduct the first empirical analysis of the relationship between ongoing civil war and coup activity, finding (1) war increases the risk of a coup attempt, though (2) war-time coup attempts are significantly less likely to be successful, and (3) the risk of war-time coup is much higher when states face stronger rebel groups that pose greater threats to the political survival of the incumbent government. We attribute these findings to the pernicious effect of ongoing war on the welfare of the military elites and soldiers who have the greatest capacity to execute a coup attempt. As war diminishes their welfare and creates uncertainty about the future of the state, potential plotters become more willing to accept riskier coup attempts than they might plot during peace-time. Coup motivations are greatest when incumbents are more likely to lose their wars, and this causes coup plotters to attempt more and riskier coups when rebels are relatively strong.