Russian speakers make up the biggest group of foreign-language speakers in Finland. Their use of Finnish words in Russian discourse can be interpreted as an example of multilingual practices, such as code-switching. It can also be viewed as an example of how loanwords are assimilated. While speakers of Russian in Finland are part of a worldwide internet community, they also represent a local community that can have a language form of its own. This article presents an analysis of about 500 cases of Finnish lexical items and word combinations usage in written Russian (260 different lemmas). The material for the research was selected from written internet discourse of a Russophone community on Facebook, a social media platform. Members of this community are Russian women who have been living in Finland for some time. The Finnish words were studied in the context of posts and replies to them. The 475 Finnish words found amounted to 4 % of the total 12,022 words used in the source. The analysis of the material took into account semantic and grammatical features of the items. Semantic features included the categories of proper nouns, terms and other words related to life in Finland. The grammatical analysis began by studying the choice of writing system, i.e. whether the units retained their original spelling which is either in Latin or in Cyrillic. After that, the Finnish words that had been transliterated were studied for the presence or lack of declension as compared to the Russian norm in similar uses. It was suggested that the tendency not to decline Finnish words written both in Cyrillic and Latin in the discourse also affected the syntactic positions in which they were used, making positions that did not require declension overrepresented. The number of examples subjected to the assimilation rules for loanwords in Russian (transliteration and using declension) was small. Therefore, most of the examples represent code-switching, a natural consequence of those living in Finland, and provide evidence for the existence of a local version of Russian.