diff --git a/libsrc/meshing/curvedelems.cpp b/libsrc/meshing/curvedelems.cpp
index 70031bdd..96e05a9d 100644
--- a/libsrc/meshing/curvedelems.cpp
+++ b/libsrc/meshing/curvedelems.cpp
@@ -1936,7 +1936,7 @@ namespace netgen
 
   template <typename T>
   void CurvedElements :: 
-  CalcElementDShapes (SurfaceElementInfo & info, const Point<2,T> xi, MatrixFixWidth<2,T> dshapes) const
+  CalcElementDShapes (SurfaceElementInfo & info, const Point<2,T> xi, MatrixFixWidth<2,T> & dshapes) const
   {
     const Element2d & el = mesh[info.elnr];
     ELEMENT_TYPE type = el.GetType();
@@ -2981,7 +2981,7 @@ namespace netgen
 
   template <typename T>
   void CurvedElements :: 
-  CalcElementDShapes (ElementInfo & info, const Point<3,T> xi, MatrixFixWidth<3,T> dshapes) const
+  CalcElementDShapes (ElementInfo & info, const Point<3,T> xi, MatrixFixWidth<3,T> & dshapes) const
   {
     // static int timer = NgProfiler::CreateTimer ("calcelementdshapes");
     
diff --git a/libsrc/meshing/curvedelems.hpp b/libsrc/meshing/curvedelems.hpp
index f95756c5..edf4a1e3 100644
--- a/libsrc/meshing/curvedelems.hpp
+++ b/libsrc/meshing/curvedelems.hpp
@@ -212,7 +212,7 @@ private:
   void CalcElementShapes (ElementInfo & info, Point<3,T> xi, TFlatVector<T> shapes) const;
   void GetCoefficients (ElementInfo & info, Vec<3> * coefs) const;
   template <typename T>  
-  void CalcElementDShapes (ElementInfo & info, const Point<3,T> xi, MatrixFixWidth<3,T> dshapes) const;
+  void CalcElementDShapes (ElementInfo & info, const Point<3,T> xi, MatrixFixWidth<3,T> & dshapes) const;
 
   template <typename T>
   bool EvaluateMapping (ElementInfo & info, const Point<3,T> xi, Point<3,T> & x, Mat<3,3,T> & jac) const;  
@@ -233,7 +233,7 @@ private:
   template <int DIM_SPACE>
   void GetCoefficients (SurfaceElementInfo & elinfo, NgArray<Vec<DIM_SPACE> > & coefs) const;
   template <typename T>
-  void CalcElementDShapes (SurfaceElementInfo & elinfo, const Point<2,T> xi, MatrixFixWidth<2,T> dshapes) const;
+  void CalcElementDShapes (SurfaceElementInfo & elinfo, const Point<2,T> xi, MatrixFixWidth<2,T> & dshapes) const;
 
   template <int DIM_SPACE, typename T>
   bool EvaluateMapping (SurfaceElementInfo & info, const Point<2,T> xi, Point<DIM_SPACE,T> & x, Mat<DIM_SPACE,2,T> & jac) const;