diff --git a/lemon/cost_scaling.h b/lemon/cost_scaling.h
--- a/lemon/cost_scaling.h
+++ b/lemon/cost_scaling.h
@@ -325,6 +325,10 @@
 
     /// @}
 
+  protected:
+
+    CostScaling() {}
+
   public:
 
     /// \brief Constructor.