diff --git a/Kinetic_data_structures/include/CGAL/Kinetic/IO/internal/Qt_widget_2_core.h b/Kinetic_data_structures/include/CGAL/Kinetic/IO/internal/Qt_widget_2_core.h
index a0d359b72c1..2003550d605 100644
--- a/Kinetic_data_structures/include/CGAL/Kinetic/IO/internal/Qt_widget_2_core.h
+++ b/Kinetic_data_structures/include/CGAL/Kinetic/IO/internal/Qt_widget_2_core.h
@@ -25,6 +25,7 @@
 #include <CGAL/IO/Qt_widget.h>
 #include <qmainwindow.h>
 #include <CGAL/Kinetic/Listener.h>
+#include <CGAL/Kinetic/Ref_counted.h>
 
 namespace CGAL
 {