According to rational adaptation approaches of language processing, readers adjust their expectations of upcoming information depending on the distributional properties of the preceding language input. However, adaptation to sentence structures has not been systematically attested, especially not in second-language (L2) processing. To further our understanding of adaptive processes, we recorded electroencephalogram (EEG) from L1-Mandarin-L2-English speakers while they read English sentences containing a coordination ambiguity. This ambiguity was always resolved toward a less-preferred clausal coordination in the first half of the study, and towards a noun-phrase coordination in the second half. Group-level results suggest that L2 readers adapted but at a slow rate and a coarse level. Individuals differed in that some changed their processing strategies, and some did not. These findings suggest that adaptation is not a direct function of fine-grained input distributions, and are problematic for the idea that adaptation is important for language learning.