diff --git a/include/wx/msw/dialog.h b/include/wx/msw/dialog.h
index 9e13ae773f..31326c37c7 100644
--- a/include/wx/msw/dialog.h
+++ b/include/wx/msw/dialog.h
@@ -74,7 +74,7 @@ public:
     // -------------------------------
 
     // override some base class virtuals
-    virtual bool Show(bool show);
+    virtual bool Show(bool show = TRUE);
 
     // event handlers
     bool OnClose();