This paper deals with some particularly interesting o-spellings attested in Latin inscriptions dating back to the late Republican age (and to the first Imperial period) and attempts to determine whether they may provide some evidence of an anticipation of the (Proto) Romance merger of the Classical Latin back-vowels /oː/ and /u/ as a close /o/. All the inscriptions have been analysed in detail by taking into account the dating, geographical origin and typology of the single epigraph, while particular attention has been paid to the possible presence (or absence) of other deviant spellings within the same texts. The results suggest that the phenomenon investigated here might actually date back to the late Republican age, at least within some substandard varieties of the language.