Inflection impairments are commonly noted in aphasia, particularly non-fluent variants, where descriptions of such difficulties often focus on inflection omission. This aligns with rule-based theory, in which inflected forms should be more difficult to produce than their uninflected counterparts. Recent studies address noun inflection for number and potential effects of the relative frequency of singular and plural forms (dominance effects). However, none examine number errors qualitatively or in spontaneous speech. We present quantitative and qualitative analyses of such errors in nouns produced by twelve people with aphasia in spoken Cinderella narratives, examining: error rate; error types and nouns involved; relationship between error production and dominance; and speakers’ consistency with error production and flexibility in varying the noun forms concerned. Twelve unimpaired speakers provide comparison data. While error rates were low, arguably more important is error type. Singularisation and pluralisation errors were observed, all on regular nouns and involving production of the dominant form. The pluralisation errors, all occurring on references to Cinderella’s glass slipper, arguably challenge rule-based predictions that the singular is easier to retrieve than the plural. We suggest constructivist, usage-based theory as a promising framework to characterise such productions. Implications for aphasiology and clinical practice are also discussed.