In 1952 Roman Jakobson (1896-1982) gave the first comprehensive exposition of his theory of “distinctive features”. The Danish phonetician and general linguist Eli Fischer-Jørgensen (1911-2010) was an important discussion partner of Jakobson’s for some thirty years. You may follow their exchange of ideas in a correspondence which ranges from 1949 until Jakobson’s death in 1982 (Bank Jensen & D’Ottavi, 2020). Fischer-Jørgensen always acknowledged her debt to Jakobson’s work; but was there also some influence the other way around? Based on Koerner’s (1989) guideline for defining the term “influence” in the history of linguistics, it is discussed which importance Fischer-Jørgensen had for Jakobson in the decade 1952-62, beyond what can be seen directly from his quotations of her. It is argued: that Fischer-Jørgensen’s critical input had an effect on some specific issues in the Jakobsonian expositions of the “distinctive feature” theory; that her suggestions had some influence on his use of theoretical concepts; and finally that she was an important figure when he took over as a chairman of the International Congresses of Phonetic Sciences.