diff --git a/dune/gfe/skewmatrix.hh b/dune/gfe/skewmatrix.hh
index 5b28a48050729afd8897ec71cf865a3f3a13be8d..632d26851f537d6e51f2f9e067bf1b7f0400f337 100644
--- a/dune/gfe/skewmatrix.hh
+++ b/dune/gfe/skewmatrix.hh
@@ -40,7 +40,7 @@ public:
     }
    
     /** \brief Embedd the skey-symmetric matrix in R^3x3 */ 
-    Dune::FieldMatrix<T,3,3> toMatrix()
+    Dune::FieldMatrix<T,3,3> toMatrix() const
     {
         Dune::FieldMatrix<T,3,3> mat;
         mat = 0;