The article deals with the question of linguistic interference among Slavic languages at the example of Choroszczynka, a bilingual village in Biała Podlaska County, Lublin Voivodeship. The presentation of two complete questionnaires for the Slavic Linguistic Atlas (OLA), Polish and Ukrainian, not only makes it possible to capture grammatical and lexical peculiarities of both sets assigned to individual dialects, but also reveals carelessness of the fi eldworkers who collected the data. This, in turn, contributed to such an interpretation of dialectal data presented in OLA maps which does not refl ect linguistic reality.