Linguistic distance in dominant-language/heritage-language (DL/HL) dyads can manifest itself as a difference in morphosyntactic structure and complexity. In the majority of dyads previously explored in the literature it has been observed that HLs undergo some morphological simplification. In some cases this is attributable to the DL being morphologically simpler than the HL; in fact most of the research has been done on English as the DL (Scontras & Putnam 2020). In this presentation I investigate a novel language dyad: heritage Tashelhiyt Berber and dominant Moroccan Arabic. Both languages belong to the Afro-Asiatic language group but Tashelhiyt is a Berber language whereas Arabic is Semitic.  In this dyad both languages show comparable complexity which makes it harder to predict the effects or the direction of simplification usually observed in better-studied DL/HL pairs. I compare these languages with respect to the Anti-Agreement Effect (AAE) a phenomenon productive in Berber languages but absent in Arabic and Semitic ones. Under the AAE subject-verb agreement is suppressed whenever the subject undergoes A-bar movement for instance in subject relative clauses (Ouhalla 1993) which are the focus of the study. The main question was whether subject-verb agreement would be maintained if the two languages differ in its distribution. There are three possible outcomes that may arise. The overmarking outcome is when a form that is absent in the heritage language is added by the heritage speaker. An instance of this would be adding a rule of affixation that is not found in the baseline. Undermarking is when a form found in the baseline is not produced by the heritage speaker. Another possible outcome is that there is faithfulness to the baseline. Here the speakers were found to generally overmark subject agreement including relative clauses where it is ungrammatical for the baseline speakers to do so. However I contend that the syntactic structure of the relative clause was maintained. One possible reason for the missing Anti-Agreement rule can be due to pressures from paradigm uniformity as well as the higher frequency of subject-agreeing constructions in both languages. The data was collected in Casablanca Morocco. A language background questionnaire was preliminarily administered to all participants both heritage speakers and Tashelhiyt-dominant bilinguals. Production data includes spontaneous narratives based on a silent cartoon clip and relative clauses elicited in a picture-disambiguation task (25 HLs 11 native Tashelhiyt controls). In terms of AAE 7 HL speakers systematically overmarked agreement. Overmarking was also present albeit to a lesser degree in the speech of the remaining eighteen heritage speakers although their fluency was significantly higher than that of the consistent overmarkers. I thus suggest that in equally complex dyads from typologically distant languages e.g. Berber and Arabic maintenance of the heritage language can still be challenged and influenced by aspects such as genetic distance here exemplified in AAE as well as additional factors such as paradigm uniformity pressures and frequency of exposure to the heritage language. The latter factor sets apart the more error-prone heritage speakers from the less error-prone ones.

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