The present study explores the notion of lexical diffusion in relation to an ongoing change in Modern French nasal vowels. Data are interviews with 42 Parisians, recorded in 1972–74 and 1989–93. We start with the notion that sound change ought to be regular, according to the classification of Labov (1994): that is, being a phonetically gradual change, it should be lexically abrupt. The first part of our analysis, which includes more than 10,000 nasal vowel tokens, seems to indicate an influence of factors compatible with the hypothesis of regular sound change (i.e., stress and phonetic surroundings). A closer look at the vowel /[vowel symbol]/, however, reveals an independent lexical and grammatical conditioning, one not entirely explicable in terms of stress or phonetics. As other studies have shown (Krishnamurti, 1998; Yaeger-Dror, 1996), gradual phonetic change might show lexical irregularities, a fact which calls for a revision of Labov's classification.