Second language (L2) learners stand to gain substantially from mastering a wide range of multiword expressions (MWEs), and several studies have examined the benefits of language courses that regularly draw learners' attention to MWEs. However, most of these studies focused on the learners' retention of the MWEs included in the course materials and did not examine a potential broader and longer term effect. In the present study, upper-intermediate students of English (N = 54) attended extracurricular classes over the course of 11 weeks (40 minutes per week) in which they either extracted MWEs from texts or engaged only in content-related activities. Outside the context of the experiment, the students occasionally wrote essays as part of their regular L2 curriculum. One of these essays was collected before the intervention, another shortly afterward, and a third 5 months later. Three coders independently identified MWEs in these essays. Both postcourse essays written by the students who had focused on MWEs were found to be richer in MWEs than those written by the comparison group. The difference was only in part due to a greater use of items encountered in the course texts, suggesting a broader and longer term effect on the students' autonomous acquisition of MWEs.