There is evidence that orthographic knowledge can influence on-line spoken-word recognition. Interestingly, when graphic and phonetic codes are not congruent due to the application of phonological alternation processes, people report hearing sounds that are matched to graphic (underlying), not phonetic codes (Hallé et al. in J Mem Lang 43:618-639, 2000). It is, however, not known whether the same effect arises in the processing of a non-native language (L2). In the present study, advanced Mandarin learners of Korean as well as native Korean listeners performed a phoneme monitoring task using words undergoing obstruent nasalization in Korean. The results showed that orthographic information dominated the phonetic judgments of the native Korean listeners, while the Mandarin learners' judgments relied more on the phonetic input. These results suggest that even the lexical access of highly experienced L2 learners differs from that of native speakers and that advanced learners still have difficulty employing orthographic information to access the L2 lexicon.