The study of more than 100 skeletal remains of Hispanochampsa muelleri Kälin, 1936, from the Oligocene of El Talladell (Lleida Province, Catalonia, Spain), has been decisive in revealing misinterpretations about its anatomy and phylogenetic position. Hispanochampsa muelleri is shown to be a member of the clade Diplocynodontinae, and is here considered a junior synonym of Diplocynodon. This analysis provides strong evidence for this monophyletic grouping, which is made up of the species Baryphracta deponiae, Diplocynodon darwini, Diplocynodon muelleri, D.tormis, D. ratelii, and D.hantoniensis. All of these species bear ventral osteoderms with paired ossifications, and a deep posterior tip of the iliac blade, which are synapomorphies of Diplocynodontinae. However, the interrelationships of the Diplocynodontinae remain unresolved. D. muelleri shares with D. hantoniensis, D. tormis, and D. ratelii the presence of an enlarged jugal foramen, and the particular dentary occlusion in line with the maxillary tooth row. It is highly likely that the two Spanish species, Diplocynodon muelleri and Diplocynodon tormis, were close relatives.