This article investigates the use and frequency of what I refer to as the K-suffixes -ō/-ū/-o in the Shirazi dialects, namely, Old and Modern Shirazi. It shows that the use of K-suffixes as definiteness markers is more highly developed in Modern Shirazi than in Old Shirazi. In Old Shirazi, the K-suffix, with its original evaluative meaning, demonstrated some degree of multi-functionality. This has mostly been lost in Modern Shirazi, and the suffix is now used to express definiteness. The high frequency of use of the K-suffix appears to be independent of genre, speaker, and speech setting. Data from a corpus of written texts in Old Shirazi, mainly comprised of poems, are quantitatively analysed, along with data from a corpus of spoken Shirazi narratives and data from a questionnaire answered by ten speakers. The results show that an evaluative suffix can develop into a definiteness marker by passing through a stage of combination with deictic markers, which paves the way for extending the use of the K-suffix to include non-deictic anaphoric tracking. This article concludes that the development of definiteness marking can proceed down a pathway that is distinct from the one normally assumed for demonstrative-based definiteness marking, even if the endpoint may be similar. The detailed documentation of this process presented here is a further contribution to Iranian studies, and augments the small group of well-documented cases of a non-demonstrative origin of definiteness marking cross-linguistically.