The current study investigates cross-linguistic influence of second language (L2) learning on native language (L1) processing of morphosyntactic variation in proficient L2 learners immersed in their L1. Despite Spanish pre- and postverbal clitic pronoun positions being grammatical in complex verb phrases, preferences of use have been well attested in naturalistic language production. To examine whether those preferences obtain for comprehension in monolinguals, as well as how those preferences might be modulated by learning an L2 with fixed pronoun positions, we administered a self-paced reading experiment to 20 Spanish monolinguals as well as 22 proficient learners English (L1 Spanish). The results of a Bayesian mixed effects regression analysis suggest that preferences in production are echoed in comprehension—but only for the monolingual group. We find support for facilitation in the bilingual group precisely where both languages overlap, as well as evidence that bilinguals may not use clitic position as a reliable cue at all. We interpret the results as evidence that learning an L2 that lacks variation for a particular feature may lead to reduced sensitivity to that feature as a cue in an analogous L1 structure. We situate these results in an experience-based, shared-syntax account of language processing.