The present study examined language comprehension in Autism Spectrum Disorder (ASD) in light of monitoring. It was studied whether individuals with ASD monitor their language perception, and whether monitoring during language perception could be modulated with instructions. We presented higher-level (semantic) linguistic violations and lower-level (orthographic) linguistic violations in a free reading condition and in an instructed condition, recording event-related potentials. For control participants, a monitoring response as tapped by the P600 effect was found to semantically and orthographically incorrect input in both conditions. For participants with ASD, however, a monitoring response to semantically implausible input, tapped by the P600, was found only in the instructed condition. For orthographic errors monitoring was observed both in the free reading and in the instructed condition. This suggests that people with ASD are less inclined than typical individuals to monitor their perception of higher-level linguistic input, but that this can be enhanced with instructions.