Prosody facilitates listeners’ segmentation of the speech stream into a sequence of words and phrases. With regard to speech timing, vowel lengthening is interpreted as a cue to an upcoming boundary, in accordance with the iambic-trochaic law. However, the impact of consonant lengthening on segmentation, in the absence of other boundary cues, has not been tested. In a series of artificial language learning experiments, we examined how durational variation affects listeners’ extraction of novel trisyllables defined by transition probabilities. In line with previous research, syllables containing lengthened vowels were interpreted by listeners as word-final. However, syllables with lengthened onset consonants were interpreted as word-initial. Thus, the structural interpretation of durational variation depends upon localization: longer vowels cue a following boundary; longer consonants cue a preceding boundary.