diff --git a/source/blender/makesrna/intern/rna_mesh.c b/source/blender/makesrna/intern/rna_mesh.c
index 37c02367f05..0cdf3c4b590 100644
--- a/source/blender/makesrna/intern/rna_mesh.c
+++ b/source/blender/makesrna/intern/rna_mesh.c
@@ -725,7 +725,7 @@ static void rna_MeshPolygon_material_index_set(PointerRNA *ptr, int value)
   Mesh *mesh = rna_mesh(ptr);
   int *material_indices = BKE_mesh_material_indices_for_write(mesh);
   const int index = rna_MeshPolygon_index_get(ptr);
-  material_indices[index] = value;
+  material_indices[index] = max_ii(0, value);
 }
 
 static void rna_MeshPolygon_center_get(PointerRNA *ptr, float *values)