Arabic broken plural morphology has been given a templatic treatment with a CVCVVCVVC template suprafixed to the skeleton of the singular (McCarthy 1983, McCarthy and Prince 1990). The Prosodic Morphology Hypothesis consistent with the iambic foot and extrametricality applies in the formation of the plural and places strong restrictions on the shapes of Arabic broken plural nouns. This paper presents cases where at a first glance the formation of these stems is not only restricted to its prosodically characterized sub-domain but also inflectional morphology out of it. Within a Distributed Morphology framework, I argue that these can be accounted for with the assumption of a null NUM that conditions the allomorphy on the stem that will be inserted. The consequences of this are that morphosyntactic features in the underlying structure first define the conditions of the minimal word followed by mapping of its contents to the iambic foot providing evidence for the syntax-morphology interaction that feeds the phonological component.