Theorists of non-territorial autonomy (NTA) have argued that one of its weaknesses is that it essentialises ethnicity and thereby potentially increases societal tensions. This article challenges this view by analysing cultural autonomy legislation in interwar Estonia, particularly national registers of minority self-governments. It shows that while the constitutional right to subjective ethnic self-identification was abolished several years after the implementation of cultural autonomy, the core reason for the abolition was the legal importance of ethnicity and bureaucratic practices of ethnicity determination that existed years before the autonomy was implemented. National registers had a potential to be based on subjective self-identification, yet lawmakers abandoned this principle when they adapted the autonomy legislation to existing bureaucratic practices stemming from tense ethnic relations. Thus, the article argues that associating NTA with the essentialisation of ethnicity is misleading and suggests that instrumental considerations of relevant actors and social contexts should be paid more attention instead.