This paper examines the morphological expression of dual and plural number in languages with apparent singular-dual-plural number systems and shows that the observed markedness of number features prevents them from accounting for all attested morphological patterns. I use the number systems of Slovenian, Manam and Mi'gmaq as examples for the three attested patterns I identify. I extend Nevins's (2011a) system of feature markedness to account for the Slovenian and Mi'gmaq patterns. I motivate a non-featural analysis of the Manam dual and compare its behaviour to that of non-inflectional plurals (Wiltschko 2008, Butler 2012).