Previous research has indicated that democracy decreases the risk of armed conflict, while increasing the likelihood of terrorist attacks, but we know little about the effect of democracy on violence against civilians in ongoing civil conflicts. This study seeks to fill this empirical gap in the research on democracy and political violence, by examining all rebel groups involved in an armed conflict 1989–2004. Using different measures of democracy, the results demonstrate that rebels target more civilians when facing a democratic (or semi-democratic) government. Democracies are perceived as particularly vulnerable to attacks on the population, since civilians can hold the government accountable for failures to provide security, and this provides incentives for rebels to target civilians. At the same time, the openness of democratic societies provides opportunities for carrying out violent attacks. Thus, the strength of democracy—its accountability and openness—can become an Achilles heel during an internal armed conflict.