diff --git a/dumux/boxmodels/common/boxmodel.hh b/dumux/boxmodels/common/boxmodel.hh
index 4c724323a374da0d033d63b9f0f2d2c0d60473c2..a3df8814baaccac8000138d3e5338a1cdada6b72 100644
--- a/dumux/boxmodels/common/boxmodel.hh
+++ b/dumux/boxmodels/common/boxmodel.hh
@@ -644,11 +644,11 @@ public:
 
         for (int i = 0; i < numEq; ++i) {
             std::ostringstream oss;
-            oss << "x_" << i;
+            oss.str(""); oss << "x_" << i;
             writer.attachVertexData(*x[i], oss.str());
-            oss.clear(); oss << "delta_" << i;
+            oss.str(""); oss << "delta_" << i;
             writer.attachVertexData(*delta[i], oss.str());
-            oss.clear(); oss << "defect_" << i;
+            oss.str(""); oss << "defect_" << i;
             writer.attachVertexData(*def[i], oss.str());
         }