One of the more challenging research issues in the context of Assured Forwarding (AF) is the fair distribution of bandwidth among aggregates sharing the same AF class. Several studies have shown that the number of microflows in aggregates, the round trip time, the mean packet size and the TCP/UDP interaction are key factors in the throughput obtained by aggregates using this architecture. In this paper, we propose the Unbiased RIO (URIO) scheme, an enhanced RIO technique that improves fairness requirements among heterogeneous aggregates in AF-based networks. We validate URIO behaviour through simulation. Simulation results show how our proposal mitigates unfairness under many different circumstances.