The present study investigated whether L1 and L2 Spanish speakers show sensitivity to matching/mismatching syllable structure and consonant sonority in lexical segmentation in Spanish. 81 English–Spanish learners and 72 Spanish–English learners completed a fragment- monitoring task. They listened to lists of Spanish words as they saw a CV or CVC syllable (e.g., “pa” or “pal”) and pressed a button when the word began with the syllable shown on the screen. The task manipulated syllable structure (CV or CVC) and consonant sonority (fricative, nasal, or liquid) of target syllables and carrier words. Target syllables either matched or did not match the structure of the first syllable in target carrier words (e.g., “pa—pa.lo.ma”; “pa—pal.me.ra”). The results showed that consonant sonority modulated sensitivity to syllable structure in both groups of participants. Spanish–English learners responded faster to matching syllable structure in words that had a fricative or a nasal as the second consonant, and English–Spanish learners responded faster only with a fricative consonant. Higher L2 Spanish proficiency correlated with faster target-syllable identification, but sensitivity to matching/mismatching structure did not vary as a function of proficiency. The study highlights the influence of phonetic factors in the development of L2 lexical segmentation routines.