The present study investigates whether lexical frequency can be increased experimentally, and whether an increase in lexical frequency facilitates L2 morphological processing. English L2 learners of Spanish were randomly assigned to either a treatment or control group. Both groups completed a pre/post lexical decision task containing L2 words with either two or three morphemes, and a pre/post lexical frequency task. In addition, the treatment group completed four sessions in which they read texts containing low frequency words. Linear mixed models and Bayes factors were used to analyze participants’ performance.Both groups took significantly longer to process morphologically complex words with three than with two morphemes at pretest. While this pattern was observed also at posttest for the control group, the treatment group took roughly the same to process both types of words following training. Taken together, the findings suggest that an increased exposure to low-frequency L2 words switches learners’ morphological computation strategies from decomposition to whole word processing. While previous cross-sectional studies have assessed the role of frequency on L2 morphological decomposition, this has not been confirmed by longitudinal data. The results support hybrid word recognition models claiming that frequency modulates morphological computation.