Although semantic influences on verbal short-term memory (STM) performance are well-established, substantially less research has studied the influence of syntactic representation. In the present study, syntactic and semantic factors were manipulated in order to explore how both interact to influence verbal STM. Subjects performed immediate, serial recall on lists of six Dutch words composed of three sets of adjective-noun pairs, where the nouns were either common (‘de’) or neuter (‘het’) gender. The grammaticality of the word pairs was manipulated through the morphological agreement between the adjectives and nouns (either legal of illegal), and the semantics by creating more or less meaningful word pairs (e.g., big bucket vs. grateful bucket). Syntactic and semantic factors were fully crossed within-subjects and within-items yielding a 2 (Grammatical) X 2 (Meaningful) X 2 (Noun Gender) design. Results on serial order memory accuracy revealed that both grammaticality and meaningfulness improved performance, and that the factors interacted, such that the beneficial effects of grammaticality were only present for lists of meaningful items. The present results thus demonstrate that while something as simple as morphological agreement (a long-term, syntactic constraint) can improve verbal STM performance, it only seem to do so in the presence stronger semantic constraints.