diff --git a/include/osgGA/MultiTouchTrackballManipulator b/include/osgGA/MultiTouchTrackballManipulator
index ba70f310e..6598e6e6e 100644
--- a/include/osgGA/MultiTouchTrackballManipulator
+++ b/include/osgGA/MultiTouchTrackballManipulator
@@ -36,7 +36,7 @@ class OSGGA_EXPORT MultiTouchTrackballManipulator : public TrackballManipulator
 
     protected:
 
-        void handleMultiTouchDrag(const GUIEventAdapter* now, const GUIEventAdapter* last, const double eventTimeDelta);
+        virtual void handleMultiTouchDrag(const GUIEventAdapter* now, const GUIEventAdapter* last, const double eventTimeDelta);
 
         osg::ref_ptr<GUIEventAdapter> _lastEvent;
 };