Dinka (Nilotic, South Sudan) has been cited as a challenge for item-based approaches to morphology, since its inflectional system is primarily expressed through changes to the root (e.g. Aronoff & Fudeman 2011:54; Inkelas 2014:72; Arkadiev & Klamer 2018:450), including lengthening, shortening, raising, lowering, as well as alternations in voice and tone. Number morphology on nouns is particularly difficult, because these changes frequently do and do not co-occur in number marking, potentially requiring a multitude of autosegmental affixes. As a result, Dinka plurals have been argued to be essentially fully irregular (Ladd et al. 2009; Andersen 2014). This talk reports on joint work with Zhouyi Sun (QMUL) demonstrating that Dinka number morphology is nonetheless concatenative and regular, with all roots combining with a single floating affix drawn from a small inventory. First, Dinka is synchronically a tripartite number system, contra Andersen (2014). Applying insights from Andersen (1993, 2017) on vowel grades and Gjersøe (2020) on tone in Nuer, we argue that Dinka nouns can be sorted into three number classes, each with three conjugation classes, within which number exponents are predictable.