diff --git a/src/widgets/newgrf_widget.h b/src/widgets/newgrf_widget.h
--- a/src/widgets/newgrf_widget.h
+++ b/src/widgets/newgrf_widget.h
@@ -14,7 +14,7 @@
 #include "../textfile_type.h"
 
 /** Widgets of the #NewGRFParametersWindow class. */
-enum NewGRFParametersWidgets {
+enum NewGRFParametersWidgets : WidgetID {
 	WID_NP_CAPTION,          ///< Caption of the window.
 	WID_NP_SHOW_NUMPAR,      ///< #NWID_SELECTION to optionally display #WID_NP_NUMPAR.
 	WID_NP_NUMPAR_DEC,       ///< Button to decrease number of parameters.
@@ -32,7 +32,7 @@ enum NewGRFParametersWidgets {
 };
 
 /** Widgets of the #NewGRFWindow class. */
-enum NewGRFStateWidgets {
+enum NewGRFStateWidgets : WidgetID {
 	WID_NS_PRESET_LIST,       ///< Active NewGRF preset.
 	WID_NS_PRESET_SAVE,       ///< Save list of active NewGRFs as presets.
 	WID_NS_PRESET_DELETE,     ///< Delete active preset.
@@ -63,7 +63,7 @@ enum NewGRFStateWidgets {
 };
 
 /** Widgets of the #SavePresetWindow class. */
-enum SavePresetWidgets {
+enum SavePresetWidgets : WidgetID {
 	WID_SVP_PRESET_LIST, ///< List with available preset names.
 	WID_SVP_SCROLLBAR,   ///< Scrollbar for the list available preset names.
 	WID_SVP_EDITBOX,     ///< Edit box for changing the preset name.
@@ -72,7 +72,7 @@ enum SavePresetWidgets {
 };
 
 /** Widgets of the #ScanProgressWindow class. */
-enum ScanProgressWidgets {
+enum ScanProgressWidgets : WidgetID {
 	WID_SP_PROGRESS_BAR,  ///< Simple progress bar.
 	WID_SP_PROGRESS_TEXT, ///< Text explaining what is happening.
 };