Do democracies aid rebels fighting against sister democracies? Scholarship on the democratic peace theory has demonstrated that, while they refrain from fighting interstate wars against one another, democracies engage in hostile acts short of war with other elected regimes such as militarized interstate disputes and covert efforts at regime change. Does this aggression extend to backing rebel groups? We hypothesize that democracies generally avoid assisting rebels battling elected governments, which we term the “democratic embargo.” This effect, however, can be trumped in the case of a serious rivalry between democracies where a potential patron has weak democratic institutions. We test this thesis with a dataset of foreign aid to rebels in civil wars from 1945-2011 and a case study of Pakistani aid to rebels in India. The results suggest that the democratic embargo is real but not an iron law. The exceptions are mainly drawn from a handful of instances of serious rivalry, especially in South Asia. There are significant implications for the democratic peace, the evolution and outcome of civil wars, and the capacity of democracies to fight insurgencies.