The aim of the present paper is to analyse a 2008 translation of one of the most important texts written by E.T.A. Hoffmann Nussknacker und der Mäusekönig in translation by E. Zarych and published by the Cracow Instytut Baśni. The analysis focuses on grammatical errors and proves that (descriptive) grammar constitutes one of the fundaments of a successful (literary) translation. The listed types of mistakes concern both morphology and syntax and prove that a lack of grammar knowledge might lead to profound alterations of the author’s message, lack of logic in the text and deviations from the original.