diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -24,6 +24,7 @@
 #include "core/alloc_func.hpp"
 #include "string_func.h"
 #include "gfx_func.h"
+#include "widgets/dropdown_func.h"
 
 #include "table/sprites.h"
 #include "table/strings.h"