In spoken French, the phonological processes of liaison and resyllabification can render word and syllable boundaries ambiguous. In the case of liaison, for example, the final /n/ of the masculine indefinite article un [œ̃] is latent in isolation or before word beginning with a consonant (un stylo [œ̃.sti.lo] 'a pen'); however, when followed by a vowel-initial word the /n/ surfaces and is resyllabified as the onset of that word (un ami [œ̃.na.mi] 'a pen'). Thus, the phrases un air 'a melody' and un nerf 'a nerve' are produced with identical phonemic content and syllable boundaries [œ̃.nɛʁ]. Some research has suggested that speakers of French give listeners acoustic cues to word boundaries by varying the duration of consonants that surface in liaison environments relative to consonant produced word-initially. Production studies (e.g. Wauquier-Gravelines 1996; Spinelli et al. 2003) have demonstrated that liaison consonants (e.g. /n/ in un air) are significantly shorter than the same consonant in initial position (e.g. /n/ in un nerf). Studies on the perception of spoken French have suggested that listeners exploit these durational differences in the segmentation of running speech (e.g. Gaskell et al. 2002; Spinelli et al. 2003), though no study to date has tested this hypothesis directly. The current study employs a direct test of the exploitation of duration as a segmentation cue by manipulating this single acoustic factor while holding all other factors in the signal constant. Thirty-six native speakers of French and 54 adult learners of French as a second language (L2) were tested on both an AX discrimination task and a forced-choice identification task which employed stimuli in which the durations of pivotal consonants (e.g. /n/ in [œ̃.nɛʁ]) were instrumentally shortened and lengthened. The results suggest that duration alone can indeed modulate the lexical interpretation of ambiguous sequences in spoken French. Shortened stimuli elicited a significantly larger proportion of vowel-initial (liaison) responses, while lengthened stimuli elicited a significantly larger proportion of consonant-initial responses, indicating that both native and (advanced) non-native speakers are indeed sensitive to this acoustic cue. These results add to a growing body of work demonstrating that listeners use extremely fined-grained acoustic detail to modulate lexical access (e.g. Salverda et al. 2003; Shatzman & McQueen 2006). In addition, the current results have manifest ramifications for study of the upper limits of L2 acquisition and the plasticity of the adult perceptual system in that several advanced learners of French showed evidence nativelike perceptual sensitivity to non-contrastive phonological variation.