In Herodotus’ Histories, at 1.66, one reads the passive aorist indicative εὐθηνήθησαν (Ionic), or εὐθενήθησαν (Attic), depending on the spelling preferred by the editors. And in Dem. 19.231, one reads the now obelised middle or passive present infinitive †εὐθενεῖσθαι†. Because the verb εὐθηνέω/εὐθενέω, ‘to be flourishing’, which is very rare, is similar to many other stative contract verbs in εω compounded with εὖ, such as εὐδαιμονέω, εὐδοκιμέω, εὐσεβέω or εὐτυχέω, which all denote a state of being, are used absolutely or intransitively, and almost exclusively in the active voice, it seems very unlikely that it would have been used twice in the most unusual middle or passive voice instead of the expected and normal active voice. Moreover, in Dem. 19.231, the infinitive †εὐθενεῖσθαι† has been condemned by Weil and was obelised by Butcher more than a century ago, a decision recently confirmed by both MacDowell and Dilts in their respective editions of the speech On the False Embassy. Consequently, the aim of this article is to make the case against the use of mediopassive forms of the verb εὐθηνέω/εὐθενέω both in Hdt. 1.66 and in Dem. 19.231 because they are, in fact, barbarisms, and to suggest palaeographically, morphologically and semantically sound emendations that make both texts consistent and correct.