Listeners usually adjust rapidly to unfamiliar regional and foreign accents in their native (L1) language. Non-native (L2) listeners, however, usually struggle when confronted with unfamiliar accents in their non-native language. The present study asks how native language background of L2 speakers influences lexical adjustments in a novel accent of German, in which several vowels were systematically lowered. We measured word judgments on a lexical decision task before and after exposure to a 15-min story in the novel dialect, and compared German, Swedish and Finnish listeners’ performance. Swedish is a Germanic language and shares with German a number of lexical roots and a relatively large vowel inventory. Finnish is a Finno-Ugric language and differs substantially from Germanic languages in both lexicon and phonology. The results were as predicted: descriptively, all groups showed a similar pattern of adaptation to the accented speech, but only German and Swedish participants showed a significant effect. Lexical and phonological relatedness between the native and non-native languages may thus positively influence lexical adaptation in an unfamiliar accent.