diff --git a/src/window_func.h b/src/window_func.h
--- a/src/window_func.h
+++ b/src/window_func.h
@@ -63,7 +63,7 @@ void ShowVitalWindows();
  */
 void ReInitAllWindows(bool zoom_changed);
 
-void SetWindowWidgetDirty(WindowClass cls, WindowNumber number, byte widget_index);
+void SetWindowWidgetDirty(WindowClass cls, WindowNumber number, WidgetID widget_index);
 void SetWindowDirty(WindowClass cls, WindowNumber number);
 void SetWindowClassesDirty(WindowClass cls);