diff --git a/src/widgets/bootstrap_widget.h b/src/widgets/bootstrap_widget.h
--- a/src/widgets/bootstrap_widget.h
+++ b/src/widgets/bootstrap_widget.h
@@ -11,19 +11,19 @@
 #define WIDGETS_BOOTSTRAP_WIDGET_H
 
 /** Widgets of the #BootstrapBackground class. */
-enum BootstrapBackgroundWidgets {
+enum BootstrapBackgroundWidgets : WidgetID {
 	WID_BB_BACKGROUND, ///< Background of the window.
 };
 
 /** Widgets of the #BootstrapErrmsgWindow class. */
-enum BootstrapErrorMessageWidgets {
+enum BootstrapErrorMessageWidgets : WidgetID {
 	WID_BEM_CAPTION, ///< Caption of the window.
 	WID_BEM_MESSAGE, ///< Error message.
 	WID_BEM_QUIT,    ///< Quit button.
 };
 
 /** Widgets of the #BootstrapContentDownloadStatusWindow class. */
-enum BootstrapAskForDownloadWidgets {
+enum BootstrapAskForDownloadWidgets : WidgetID {
 	WID_BAFD_QUESTION, ///< The question whether to download.
 	WID_BAFD_YES,      ///< An affirmative answer to the question.
 	WID_BAFD_NO,       ///< An negative answer to the question.