diff --git a/include/wx/mac/dialog.h b/include/wx/mac/dialog.h
index 11652bd281..24a6464f5d 100644
--- a/include/wx/mac/dialog.h
+++ b/include/wx/mac/dialog.h
@@ -65,7 +65,7 @@ public:
     ~wxDialog();
 
 //    virtual bool Destroy();
-    bool Show(bool show);
+    bool Show(bool show = true);
 
     void SetModal(bool flag);
     virtual bool IsModal() const;