diff --git a/src/terraform_gui.cpp b/src/terraform_gui.cpp
--- a/src/terraform_gui.cpp
+++ b/src/terraform_gui.cpp
@@ -12,6 +12,7 @@
 #include "player.h"
 #include "tile.h"
 #include "gui.h"
+#include "window_gui.h"
 #include "viewport.h"
 #include "gfx.h"
 #include "sound.h"