diff --git a/include/wx/msw/toplevel.h b/include/wx/msw/toplevel.h
index 62a4dca14f..ce10f8e628 100644
--- a/include/wx/msw/toplevel.h
+++ b/include/wx/msw/toplevel.h
@@ -60,8 +60,8 @@ public:
     virtual bool Show(bool show = TRUE);
 
     // FIXME -- not yet moved from wxFrame to wxTLW
-    virtual bool ShowFullScreen(bool show, long style = wxFULLSCREEN_ALL) {}
-    virtual bool IsFullScreen() { return FALSE; }
+    virtual bool ShowFullScreen(bool show, long style = wxFULLSCREEN_ALL) { return FALSE; }
+    virtual bool IsFullScreen() const { return FALSE; }
 
     // implementation from now on
     // --------------------------