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). (Contains 7 figures and 5 tables.)