Measurements made by the Energetic Particle Anisotropy Spectrometer (EPAS) on the International Cometary Explorer (ICE) spacecraft show that relatively abrupt changes occur in energetic heavy ion properties near the periphery of the mass-loaded flow region surrounding comet P/Giacobini-Zinner. Corresponding features are observed both inbound and outbound from the comet. As the distance to the comet decreases, a change in the ion distribution takes place over approximately 5 minutes, indicative of flow deflection away from the comet-sun axis. Shortly afterwards, the ion angular distribution broadens over a further 6 minutes, indicative of a slowing of the ion bulk flow by about 100 km s-1. Taken together with magnetic field and plasma data, these observations are suggestive of a shock wave standing in the flow.