diff --git a/src/frontends/qt/GuiToc.h b/src/frontends/qt/GuiToc.h
index f29a9af59c..48f68b3c9f 100644
--- a/src/frontends/qt/GuiToc.h
+++ b/src/frontends/qt/GuiToc.h
@@ -32,7 +32,7 @@ public:
 	GuiToc(
 		GuiView & parent, ///< the main window where to dock.
 		Qt::DockWidgetArea area = Qt::LeftDockWidgetArea, ///< Position of the dock (and also drawer)
-		Qt::WindowFlags flags = 0);
+		Qt::WindowFlags flags = nullptr);
 
 	///
 	bool initialiseParams(std::string const & data);