diff --git a/include/base_screen.h b/include/base_screen.h
index 3c8b42760e..3e4db72ae2 100644
--- a/include/base_screen.h
+++ b/include/base_screen.h
@@ -346,7 +346,7 @@ public:
      * @param iu_per_du is the number of internal units (world units) per
      *   device units (pixels typically).
      */
-    bool SetZoom( double iu_per_du );
+    virtual bool SetZoom( double iu_per_du );
 
     bool SetNextZoom();
     bool SetPreviousZoom();
diff --git a/include/class_draw_panel_gal.h b/include/class_draw_panel_gal.h
index e50d41816d..a70144f815 100644
--- a/include/class_draw_panel_gal.h
+++ b/include/class_draw_panel_gal.h
@@ -118,7 +118,7 @@ public:
     }
 
     /// @copydoc wxWindow::Refresh()
-    void Refresh( bool aEraseBackground = true, const wxRect* aRect = NULL ) override;
+    virtual void Refresh( bool aEraseBackground = true, const wxRect* aRect = NULL ) override;
 
     /**
      * Function ForceRefresh()
@@ -218,7 +218,7 @@ public:
      * Function GetDefaultCursor
      * @return the default cursor shape
      */
-    int GetDefaultCursor() const { return m_defaultCursor; }
+    virtual int GetDefaultCursor() const  { return m_defaultCursor; }
 
     /**
      * Function GetCurrentCursor
@@ -243,7 +243,7 @@ public:
     void OnEvent( wxEvent& aEvent );
 
 protected:
-    void onPaint( wxPaintEvent& WXUNUSED( aEvent ) );
+    virtual void onPaint( wxPaintEvent& WXUNUSED( aEvent ) );
     void onSize( wxSizeEvent& aEvent );
     void onEnter( wxEvent& aEvent );
     void onLostFocus( wxFocusEvent& aEvent );