For second language (L2) learners of Mandarin, mastery of lexical tones is a particularly salient challenge and many learners expend a great deal of effort trying to gain control of tones both receptively and in production. To date, little is understood about how successful they are at this task, especially in regards to the types of problems that persist for more advanced learners. At the same time, as a practical matter, it is unclear how important tone accuracy actually is for L2 speakers, i.e, how sensitive are native speakers to tone errors? The proposed study aims to explore these questions by exploiting the abilities of EEG to measure automatic online reactions to tone errors in both native and L2 listeners. Results would potentially be informative both for those interested in L2 learning problems and for those interested in how high-level predictive processes (expectations about individual speakers) can influence native and L2 language processing.