diff --git a/dune/solvers/iterationsteps/multigridstep.hh b/dune/solvers/iterationsteps/multigridstep.hh
index 73e67eac12bf58cb6a434652ac77e859714e8ab5..ed34da117e1fc49f9673720594ebce9cc53dd959 100644
--- a/dune/solvers/iterationsteps/multigridstep.hh
+++ b/dune/solvers/iterationsteps/multigridstep.hh
@@ -34,7 +34,7 @@
 
         MultigridStep(const MatrixType& mat,
                       VectorType& x,
-                      VectorType& rhs,
+                      const VectorType& rhs,
                       int mu, int nu1, int nu2,
                       LinearIterationStep<MatrixType, VectorType>* preSmoother,
                       LinearIterationStep<MatrixType, VectorType>* postSmoother,
@@ -56,7 +56,7 @@
 
         MultigridStep(const MatrixType& mat,
                       VectorType& x,
-                      VectorType& rhs) :
+                      const VectorType& rhs) :
             LinearIterationStep<MatrixType, VectorType>(mat, x, rhs),
             basesolver_(0),
             preprocessCalled(false)