The negative effect of cold working on the magnetocaloric effect across the Curie transition of Mn-based Heusler alloys is highlighted. The results of manual crushing and subsequent heat treatment on the magnetic and magnetocaloric properties of a Ni₅₀Mn₃₄In₁₆ sample are reported. Plausible explanations of the degradation of the magnetocaloric effect by cold working are discussed, on the basis of magnetic and structural measurements performed on a reference sample. The study of the connection between microstructure and magnetic properties of these materials represents a key point for the improvement of Heusler-based magnetic refrigeration.