diff --git a/src/vtk.cc b/src/vtk.cc
index 00c4a2fd5b3d1fb8462bf5ba7b19f23d3587c563..b92b06166ec6af162071d0f20fce55e85751bddb 100644
--- a/src/vtk.cc
+++ b/src/vtk.cc
@@ -6,10 +6,10 @@
 
 template <class VertexBasis, class CellBasis, class VectorType,
           class SingletonVectorType, class GridView>
-void writeVtk(VertexBasis vertexBasis, VectorType displacement,
-              SingletonVectorType state, CellBasis cellBasis,
-              SingletonVectorType stress, GridView gridView,
-              std::string filename) {
+void writeVtk(VertexBasis const &vertexBasis, VectorType const &displacement,
+              SingletonVectorType const &state, CellBasis const &cellBasis,
+              SingletonVectorType const &stress, GridView const &gridView,
+              std::string const &filename) {
   Dune::VTKWriter<GridView> writer(gridView);
 
   auto const displacement_ptr =
diff --git a/src/vtk.hh b/src/vtk.hh
index e0d1de1682257b5ca3ce6d70a947ef3ac5298fbb..9986fe9047c42dd422d41b5b2fcab990e2e49d6f 100644
--- a/src/vtk.hh
+++ b/src/vtk.hh
@@ -8,9 +8,9 @@
 
 template <class VertexBasis, class CellBasis, class VectorType,
           class SingletonVectorType, class GridView>
-void writeVtk(VertexBasis vertexBasis, VectorType displacement,
-              SingletonVectorType state, CellBasis cellBasis,
-              SingletonVectorType stress, GridView gridView,
-              std::string filename);
+void writeVtk(VertexBasis const &vertexBasis, VectorType const &displacement,
+              SingletonVectorType const &state, CellBasis const &cellBasis,
+              SingletonVectorType const &stress, GridView const &gridView,
+              std::string const &filename);
 
 #endif
diff --git a/src/vtk_tmpl.cc b/src/vtk_tmpl.cc
index 23785948c09bd10bc04d444be236a27d8d7f8a75..eac4a0ccca4f986d0877d60570e680adf55f3f82 100644
--- a/src/vtk_tmpl.cc
+++ b/src/vtk_tmpl.cc
@@ -22,7 +22,10 @@ typedef P1NodalBasis<GridView, double> P1Basis;
 typedef P0Basis<GridView, double> MyP0Basis;
 
 template void writeVtk<P1Basis, MyP0Basis, VectorType, SingletonVectorType,
-                       GridView>(P1Basis vertexBasis, VectorType displacement,
-                                 SingletonVectorType state, MyP0Basis cellBasis,
-                                 SingletonVectorType stress, GridView gridView,
-                                 std::string filename);
+                       GridView>(P1Basis const &vertexBasis,
+                                 VectorType const &displacement,
+                                 SingletonVectorType const &state,
+                                 MyP0Basis const &cellBasis,
+                                 SingletonVectorType const &stress,
+                                 GridView const &gridView,
+                                 std::string const &filename);