Opportunistic networks are partially connected wireless ad hoc networks, in which pairwise unpredicted transient contacts between mobile devices are the only opportunities for these devices to exchange information or services. Ensuring the coordination of multiple parts of a distributed application in such conditions is a challenge. This paper presents a system that can solve consensus problems in an opportunis-tic network. This system combines an implementation of the One-Third Rule (OTR) algorithm with a communication layer that supports network-wide, content-driven message dissemination based on controlled epidemic routing. Experimental results obtained with a small flotilla of smartphones are also presented, that validate the system and demonstrate that consensus can be solved effectively in an opportunistic network.