Policymakers sometimes argue that material assistance to rebels involved in a civil war can create a ‘ripe moment’ that is favorable for negotiations. Ripeness theory provides support for this idea. However, this notion has never been systematically assessed. This article evaluates this claim by using global data on negotiations in all intrastate armed conflicts from 1975 to 2009. Contrary to popular belief, the article demonstrates that external state support to rebel groups does not increase the prospect of negotiations. Instead, the results suggest that external support is likely to reduce the likelihood of negotiations between the warring parties, especially if the state sponsor is a great power. The study contributes to our understanding of civil war processes by demonstrating that military assistance hinders rather than promotes the onset of negotiations and by questioning the utility of ripeness theory as the most suitable framework for understanding this phenomenon.