diff --git a/dock_gui.c b/dock_gui.c
--- a/dock_gui.c
+++ b/dock_gui.c
@@ -10,6 +10,7 @@
 #include "gfx.h"
 #include "sound.h"
 #include "command.h"
+#include "variables.h"
 
 static void ShowBuildDockStationPicker(void);
 static void ShowBuildDocksDepotPicker(void);