Abstract In the present study we analyze how the cognitive system deals on-line with number agreement mismatches and whether this on-line process influences the off-line interpretation of the sentence. In two ERP experiments we monitored the on-line processing consequences of subject-verb agreement mismatches, focusing on the integration of a following number- marked related constituent. In Experiment 1, after initial detection of a mismatch between a plural noun phrase ( The siblings) and its singular verb, indexed by LAN + P600, ERP correlates of agreement processing difficulties were recorded on a following modifier when it was plural. In Experiment 2, after detection of the mismatch between two conjoined singular noun phrases in subject position ( The brother and the sister) and the verb, indexed by a short-lived P600, only the singular modifier showed indexes of agreement processing difficulties. These findings support the hypothesis that when processing a morphosyntactic mismatch, the cognitive system constructs on-line a well-formed internal representation of the sentence fragment. This on-line regularization allows comprehenders to easily integrate additional incoming constituents and also influences off-line interpretation of the message (Experiment 3).