Grammatical agreement phenomena such as verbal number have long been of fundamental interest in the study of second language (L2) acquisition. Previous research from the perspective of sentence processing has documented nativelike behavior among nonnative participants but has also relied almost exclusively on grammar violation paradigms. The present investigation examined the online comprehension of subject-verb number agreement by native and nonnative speakers of Mexican Spanish using the more subtle agreement attraction paradigm, with stimuli grammatical in both conditions, in addition to a nonlocal grammaticality paradigm. The results of a self-paced reading experiment confirmed that nonnatives can acquire nativelike online sensitivity to verbal number agreement, even without grammar errors, and that such sensitivity develops only at very high levels of L2 proficiency.