Adults learning a new language tend to judge unconventional utterances more leniently than fluent speakers do; ratings on acceptable utterances, however, tend to align more closely with fluent speakers. This asymmetry raises a question as to whether unconventional utterances can be statistically preempted by conventional utter- ances for adult learners. We report a preregistered study that provided undergraduates in Spanish classes with three days of exposure to conventional Spanish sentences without feedback. Judgment data reveal a significant effect of statistical preemption, particularly on intermediate learners, as predicted: Repeatedly witnessing conventional sentences led learners to subsequently judge as significantly lower the corresponding unconven- tional formulations in comparison to unrelated unconventional sentences. Current find- ings indicate that adult learners can take advantage of statistical preemption to learn the unacceptability of unconventional sentences from repeated exposure to acceptable alternatives, without explicit instruction or feedback.