diff --git a/src/core/default-value.h b/src/core/default-value.h
index 6f9f98508..08dbae285 100644
--- a/src/core/default-value.h
+++ b/src/core/default-value.h
@@ -45,6 +45,8 @@ public:
 protected:
   DefaultValueBase (const std::string &name, 
 		    const std::string &help);
+private:
+  DefaultValueBase ();
 private:
   virtual bool DoParseValue (const std::string &value) = 0;
   virtual std::string DoGetType (void) const = 0;