diff --git a/Packages/Qt_widget/demo/Qt_widget/Partition_2/Qt_widget_toolbar_layers.h b/Packages/Qt_widget/demo/Qt_widget/Partition_2/Qt_widget_toolbar_layers.h
index a65086c080b..f0c3311c810 100644
--- a/Packages/Qt_widget/demo/Qt_widget/Partition_2/Qt_widget_toolbar_layers.h
+++ b/Packages/Qt_widget/demo/Qt_widget/Partition_2/Qt_widget_toolbar_layers.h
@@ -52,6 +52,7 @@
 #include <qtoolbar.h>
 #include <qstatusbar.h>
 #include <qbuttongroup.h>
+#include <qmainwindow.h>
 
 namespace CGAL {