This paper considers an application-level multicast protocol, HBM, which can be used when native multicast routing is not available. Being purely end-to-end, application-level multicast proposals in general, and HBM in particular, are intrinsically more fragile than traditional routing solutions relying on well administered and dedicated routers. Improving their robustness is therefore of high practical importance and we believe it is a key aspect for the acceptance of the technology by end users who won't tolerate that a multi-participant video-conference session be subject to frequent cuts. In this work we identify two classes of problems that lead to packet losses, and for each class we introduce and compare several schemes. Experiments show that in both cases simple yet efficient solutions exist.