This self-paced reading study investigated the processing of case marking with the particle a in non-native Spanish. Experiment 1 tested online sensitivity to case marking on direct and indirect objects. Unlike native speakers, intermediate L2 learners showed effects only with indirect objects. For Experiment 2, direct objects were doubled with a preverbal clitic, to see if the addition was associated with more native-like processing, as has been shown in previous research with very advanced L2 learners (Jegerski, 2015). Again, online sensitivity to case marking was only observed with the ditransitive stimuli. Thus, clitic doubling only seems to make a difference at sufficiently high levels of proficiency, perhaps because of increasingly robust representations of grammatical forms in the developing L2 system.