diff --git a/opm/core/flowdiagnostics/TofDiscGalReorder.cpp b/opm/core/flowdiagnostics/TofDiscGalReorder.cpp
index 1173083c1..26f594008 100644
--- a/opm/core/flowdiagnostics/TofDiscGalReorder.cpp
+++ b/opm/core/flowdiagnostics/TofDiscGalReorder.cpp
@@ -217,7 +217,8 @@ namespace Opm
             tracerhead_by_cell_.resize(grid_.number_of_cells, NoTracerHead);
         }
         for (int tr = 0; tr < num_tracers_; ++tr) {
-            for (int i = 0; i < tracerheads[tr].size(); ++i) {
+            const unsigned int tracerheadsSize = tracerheads[tr].size();
+            for (unsigned int i = 0; i < tracerheadsSize; ++i) {
                 const int cell = tracerheads[tr][i];
                 basis_func_->addConstant(1.0, &tracer_coeff[cell*num_tracers_*num_basis + tr*num_basis]);
                 tracer_coeff[cell*num_tracers_ + tr] = 1.0;
diff --git a/opm/core/flowdiagnostics/TofReorder.cpp b/opm/core/flowdiagnostics/TofReorder.cpp
index 6f605575c..3cd0bfc2e 100644
--- a/opm/core/flowdiagnostics/TofReorder.cpp
+++ b/opm/core/flowdiagnostics/TofReorder.cpp
@@ -142,7 +142,8 @@ namespace Opm
             tracerhead_by_cell_.resize(num_cells, NoTracerHead);
         }
         for (int tr = 0; tr < num_tracers; ++tr) {
-            for (int i = 0; i < tracerheads[tr].size(); ++i) {
+            const unsigned int tracerheadsSize = tracerheads[tr].size();
+            for (unsigned int i = 0; i < tracerheadsSize; ++i) {
                 const int cell = tracerheads[tr][i];
                 tracer[num_cells * tr + cell] = 1.0;
                 tracerhead_by_cell_[cell] = tr;