Grammatical priming of picture naming was investigated in Kiswahili, which has a complex grammatical noun class system (a system like grammatical gender), with up to 15 noun classes that have obligatory agreements on adjectives, verbs, pronouns and other parts of speech. Participants heard a grammatically agreeing (concordant), nonagreeing (discordant) or neutral prime before seeing a picture of a common object and being asked to name the object. Priming was found, with naming following concordant primes being faster than naming following the neutral prime ('say'). However, more interestingly, effects were found such that where two noun classes share a prefix, the grammatical prime from each of these two noun classes also primed words that have the same prefix but are not in the same noun class, and hence for which the prime was not grammatical. It is concluded that the prime appears to be facilitating the phonological form of the prefix rather than the syntacto-semantic group of words that are known as a noun class, and that the phonological form associated with a grammatical entity may be more significant in its processing than has previously been supposed.