Corpus surveys have shown that the exact forms with which idioms are realized are subject to variation. We report a rating experiment showing that such alternative realizations have varying degrees of acceptability. Idiom variation challenges processing theories associating idioms with fixed multi‐word form units (Bobrow & Bell, 1973), fixed configurations of words (Cacciari & Tabossi, 1988), or fixed superlemmas (Sprenger, Levelt, & Kempen, 2006), as they do not explain how it can be that speakers produce variant forms that listeners can still make sense of. A computational model simulating comprehension with naive discriminative learning is introduced that provides an explanation for the different degrees of acceptability of several idiom variant types. Implications for multi‐word units in general are discussed.