diff --git a/dune/gfe/targetspacertrsolver.cc b/dune/gfe/targetspacertrsolver.cc
index c1c4d5aa53d602b0605a4ebf1bc179c066037adc..9851b6ae4b5bee5031c722e5c280a0a726af77b7 100644
--- a/dune/gfe/targetspacertrsolver.cc
+++ b/dune/gfe/targetspacertrsolver.cc
@@ -57,7 +57,7 @@ void TargetSpaceRiemannianTRSolver<TargetSpace>::solve()
     // /////////////////////////////////////////////////////
     //   Trust-Region Solver
     // /////////////////////////////////////////////////////
-    for (int i=0; i<maxTrustRegionSteps_; i++) {
+    for (size_t i=0; i<maxTrustRegionSteps_; i++) {
 
         if (this->verbosity_ == Solver::FULL) {
             std::cout << "----------------------------------------------------" << std::endl;
diff --git a/dune/gfe/targetspacertrsolver.hh b/dune/gfe/targetspacertrsolver.hh
index 8c34f20e0ce6a963156cfb43c8240fc312084579..bd3baea68fe249617b66c3ded569b1d36b514d71 100644
--- a/dune/gfe/targetspacertrsolver.hh
+++ b/dune/gfe/targetspacertrsolver.hh
@@ -61,7 +61,7 @@ protected:
     double initialTrustRegionRadius_;
 
     /** \brief Maximum number of trust-region steps */
-    int maxTrustRegionSteps_;
+    size_t maxTrustRegionSteps_;
 
     /** \brief Maximum number of multigrid iterations */
     int innerIterations_;