The purpose of this article is to illustrate how erroneous interpretations or spelling mistakes of foreign, quite often odd, place names can be used to determine relationships between manuscripts. The paper analyses three cases of false toponimy found in Onuphrius vita. One reading, pointing out the location of the monastery where Onuphrius grew up before his escape to the desert, consists of an incomprehensible string of words. The corresponding Greek text is of no help in solving the problem. Not until we examined several available Greek versions and a considerable number of Slavonic manuscripts could we reconstruct the emergence of that enigmatic toponym. The name of the well-known Egyptian city Hermopolis lacking one syllable caused confusion, and an erroneous stress mark over the Greek word (nomos) suggested a completely different sense of meaning (‘low’ instead of ‘district’). The most widely spread Slavonic version of the vita contains both of the above-mentioned slips of the pen. The defective name probably originated as far back as in one of the intermediate Greek manuscripts. It is obvious that the Slavs tried to understand the weird forms without questioning the erroneous Greek readings. We suggest a reconstruction of the conceivable original reading based on a deviating reading of a single south Slavonic (serbian) manuscript, a reading confirmed by one Greek manuscript). The Slavonic tradition also reflects two interpretations of another place name, Scete, which is used as a proper noun only in parts of the manuscripts. Further, a group of manuscripts are distinguished by an unusual and consistent, therefore conscious, replacement of the toponym Egypt. Thus far there is no explanation why this place name was censured in a subgroup of south Slavonic manuscripts. To summarize, misunderstandings and erroneous forms of toponyms veil clues about how the transmission of texts from Greek into the Slavonic tradition occurred. Such errors might contribute to the identification of translations and redactions, they can provide valuable insight into the understanding of cultural transmissions.