--- a/Framework/Common/NullValue.h	Wed Dec 16 13:59:17 2020 +0100
+++ b/Framework/Common/NullValue.h	Wed Dec 16 15:05:19 2020 +0100
@@ -23,19 +23,21 @@
 
 #include "IValue.h"
 
+#include <Compatibility.h>
+
 namespace OrthancDatabases
 {
   class NullValue : public IValue
   {
   public:
-    virtual ValueType GetType() const
+    virtual ValueType GetType() const ORTHANC_OVERRIDE
     {
       return ValueType_Null;
     }
 
-    virtual IValue* Convert(ValueType target) const;
+    virtual IValue* Convert(ValueType target) const ORTHANC_OVERRIDE;
 
-    virtual std::string Format() const
+    virtual std::string Format() const ORTHANC_OVERRIDE
     {
       return "(null)";
     }