diff --git a/src/lib_gui/qt/window/QtIndexingDialog.h b/src/lib_gui/qt/window/QtIndexingDialog.h
index 3708f11f..124c6129 100644
--- a/src/lib_gui/qt/window/QtIndexingDialog.h
+++ b/src/lib_gui/qt/window/QtIndexingDialog.h
@@ -1,6 +1,8 @@
 #ifndef QT_INDEXING_WIZARD_WINDOW_H
 #define QT_INDEXING_WIZARD_WINDOW_H
 
+#include <functional>
+
 #include "qt/window/QtWindow.h"
 
 class QLabel;