Mistrust between conflict parties after civil war is a major hurdle to sustainable peace. However, existing research focuses on elite interactions and has not examined the trust relationship between government and rank-and-file members of armed groups, despite their importance for postconflict stability. We use the unexpected decision of the Colombian government to extradite top-level former paramilitary leaders to the United States in 2008 to identify how a peace deal reversal influences ex-combatants’ trust in government. In theory, they may lose trust for instrumental reasons, if they suffer personal costs, or for normative reasons, if they think the government is failing its commitments. Using quasi-experimental survey evidence, we find that extradition decreases trust substantially among ex-paramilitaries, but not in a comparison group of ex-guerrillas not part of the same peace deal. Even though paramilitaries are seen as particularly opportunistic, our evidence suggests that normative rather than instrumentalist considerations led to trust erosion.