diff --git a/src/window_gui.h b/src/window_gui.h
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -327,7 +327,7 @@ public:
 	NWidgetStacked *shade_select;    ///< Selection widget (#NWID_SELECTION) to use for shading the window. If \c NULL, window cannot shade.
 	Dimension unshaded_size;         ///< Last known unshaded size (only valid while shaded).
 
-	int scrolling_scrollbar;         ///< Widgetindex of just being dragged scrollbar. -1 if none is active.
+	int mouse_capture_widget;        ///< Widgetindex of current mouse capture widget (e.g. dragged scrollbar). -1 if no widget has mouse capture.
 
 	Window *parent;                  ///< Parent window.
 	Window *z_front;                 ///< The window in front of us in z-order.