diff --git a/src/viewport_gui.cpp b/src/viewport_gui.cpp
--- a/src/viewport_gui.cpp
+++ b/src/viewport_gui.cpp
@@ -61,7 +61,7 @@ public:
 		if (_settings_client.gui.zoom_min == viewport->zoom) this->DisableWidget(WID_EV_ZOOM_IN);
 	}
 
-	void SetStringParameters(int widget) const override
+	void SetStringParameters(WidgetID widget) const override
 	{
 		switch (widget) {
 			case WID_EV_CAPTION:
@@ -71,7 +71,7 @@ public:
 		}
 	}
 
-	void OnClick([[maybe_unused]] Point pt, int widget, [[maybe_unused]] int click_count) override
+	void OnClick([[maybe_unused]] Point pt, WidgetID widget, [[maybe_unused]] int click_count) override
 	{
 		switch (widget) {
 			case WID_EV_ZOOM_IN: DoZoomInOutWindow(ZOOM_IN,  this); break;
@@ -117,7 +117,7 @@ public:
 		this->viewport->dest_scrollpos_y = this->viewport->scrollpos_y;
 	}
 
-	bool OnRightClick([[maybe_unused]] Point pt, int widget) override
+	bool OnRightClick([[maybe_unused]] Point pt, WidgetID widget) override
 	{
 		return widget == WID_EV_VIEWPORT;
 	}