diff --git a/dune/solvers/test/mmgtest.cc b/dune/solvers/test/mmgtest.cc
index 453775ff0fb2f494f58ef2d2fe8733389d94eb64..ea53a9fd95ffa5cf974adbda569f4734be54dd80 100644
--- a/dune/solvers/test/mmgtest.cc
+++ b/dune/solvers/test/mmgtest.cc
@@ -65,7 +65,7 @@ void solveObstacleProblemByMMGSolver(const GridType& grid, const MatrixType& mat
     mmgStep.hasObstacle_       = &hasObstacle;
 
     std::vector<BoxConstraint<typename VectorType::field_type,blockSize> > boxConstraints(rhs.size());
-    for (int i = 0; i < boxConstraints.size(); ++i)
+    for (size_t i = 0; i < boxConstraints.size(); ++i)
     {
         for (int j = 0; j < blockSize; ++j)
         {
diff --git a/dune/solvers/test/quadraticipoptsolvertest.cc b/dune/solvers/test/quadraticipoptsolvertest.cc
index 2516373f5b7690f03260e904a14955106832790c..e5f19898ed9fa6cf242c9336c6a8ca80db4bff7d 100644
--- a/dune/solvers/test/quadraticipoptsolvertest.cc
+++ b/dune/solvers/test/quadraticipoptsolvertest.cc
@@ -34,7 +34,7 @@ void solveObstacleProblemByQuadraticIPOptSolver(const GridType& grid, const Matr
 
     // create double obstacle constraints
     std::vector<BoxConstraint<typename VectorType::field_type,blockSize> > boxConstraints(rhs.size());
-    for (int i = 0; i < boxConstraints.size(); ++i)
+    for (size_t i = 0; i < boxConstraints.size(); ++i)
     {
         for (int j = 0; j < blockSize; ++j)
         {