Crosslinguistic influence has been seen in bilingual adult and child learners when compared to monolingual learners. For speakers of Light Warlpiri and Gurindji Kriol there is no monolingual group for comparison, yet crosslinguistic influence can be seen in how the speakers resolve competition between case-marking and word order systems in each language. Light Warlpiri and Gurindji Kriol are two new Australian mixed languages, spoken in similar, yet slightly different, sociolinguistic contexts, and with similar, yet slightly different, argument marking systems. The different sociolinguistic situations and systems of argument marking lead to a difference in how speakers of each language interpret simple transitive sentences in a comprehension task. Light Warlpiri speakers rely on ergative case-marking as an indicator of agents more often than Gurindji Kriol speakers do. Conversely, Gurindji Kriol speakers rely on word order more often than Light Warlpiri speakers do.