diff --git a/dune/gfe/riemanniantrsolver.cc b/dune/gfe/riemanniantrsolver.cc
index 40c3286ce3849dd5553eb81733990478e7bad8ed..818b8cd3e81fa2ab90bf26ba0b14d3a8d299791f 100644
--- a/dune/gfe/riemanniantrsolver.cc
+++ b/dune/gfe/riemanniantrsolver.cc
@@ -359,7 +359,7 @@ void RiemannianTrustRegionSolver<GridType,TargetSpace>::solve()
 
             CorrectionType gradient = rhs_global;
             for (size_t j=0; j<gradient.size(); j++)
-              for (int k=0; k<gradient[j].size(); k++)
+              for (size_t k=0; k<gradient[j].size(); k++)
                 if ((*mgStep->ignoreNodes_)[j][k])  // global Dirichlet nodes set
                   gradient[j][k] = 0;