Despite extensive theoretical and empirical research, we do not have estimations of the magnitude of sensitivity to grammatical information during L2 online processing. This is largely due to reliance on null hypothesis significance testing (Plonsky, 2015). The current meta-analysis draws on data from one elicitation technique, self-paced reading, across 57 studies (N = 3,052), to estimate sensitivity to L2 morphosyntax and how far L1 background moderates this. Overall, we found a reliable sensitivity to L2 morphosyntax at advanced proficiencies (d = 0.20, 95% CIs 0.15, 0.25), with some evidence that this was reliably lower than for native speakers (NSs). These patterns were not generally moderated by linguistic feature or sentence region. However, effects for anomaly detection were larger among NSs than L2 learners and the effects among L2 learners appeared to show a trend toward L1 influence. Finding smaller effects than in other subdomains, we provide an initial framework of reference for L2 reading time effect sizes.