In ‚Grimms’ Words‘ (‚Grimms Wörter‘), Günter Grass tells the story of the famous German scholars Jacob and Wilhelm Grimm, and combines these biographical episodes with recollections and anecdotes from his own life. While the autobiographical passages are naturally told from a first person perspective, so are the tales from the nineteenth century. Grass appears as a figure even in the fictional parts of his own work, interacts with the Grimm Brothers, and observes the events of their lives as an eye witness, blurring the lines between history and fiction, biography and autobiography: Certain scenes in ‚Grimms’ Words‘ paradoxically seem to be autobiographical as well as fictional. In this paper I develop the concept of ‘autofictional interference’ to describe this unique phenomenon, using Philipp Lejeune’s notion of ‘autobiographical pact’ as a theoretical foundation. This newly coined category is subsequently used to analyze the complex narrative structure of Günter Grass’ final work.