This article examines the case system in a fifteenth-century Utrecht manuscript. It demonstrates that there is a functional case system in the manuscript. However, it also identifies a relatively small number of mistakes – grammatical errors as well as hypercorrections – in how this case system is used. It argues that these mistakes indicate that the case system had lost its support in the underlying spoken dialect. The mistakes concern both the use of cases in the nominative and the accusative, and the use of gender markers in the genitive and the dative. By examining the mistakes in the use of cases (accusative and nominative), it is possible to determine the conditions for syncretic n-deletion in the underlying spoken dialect; and, by examining the mistakes in the use of gender markers (in the genitive and dative), it is possible to determine the expansion of masculine flexion in the genitive and dative in the underlying spoken dialect. ; This article examines the case system in a fifteenth-century Utrecht manuscript. It demonstrates that there is a functional case system in the manuscript. However, it also identifies a relatively small number of mistakes – grammatical errors as well as hypercorrections – in how this case system is used. It argues that these mistakes indicate that the case system had lost its support in the underlying spoken dialect. The mistakes concern both the use of cases in the nominative and the accusative, and the use of gender markers in the genitive and the dative. By examining the mistakes in the use of cases (accusative and nominative), it is possible to determine the conditions for syncretic n-deletion in the underlying spoken dialect; and, by examining the mistakes in the use of gender markers (in the genitive and dative), it is possible to determine the expansion of masculine flexion in the genitive and dative in the underlying spoken dialect.