Research in second language acquisition has presumed that acquiring an aspect of grammar that is a subset of a speaker's first language is difficult due to the amount and type of evidence typically available to the learner. In this paper, it is proposed that a new type of evidence may facilitate the acquisition of a subset grammar: indirect positive evidence (IPE). IPE is evidence from errors that native speakers of the learner's L2 make in the learner's native language. This paper experimentally examines whether native speakers of English can acquire the phonotactic constraints that hold of word initial clusters in Brazilian Portuguese (BP), which are a subset of English word initial clusters, using IPE only. After listening to a seven minute long dialogue of BP-accented English, participants were able to make BP-like judgements of word initial consonant clusters. This suggests that learners can rely on IPE to facilitate language acquisition.