diff --git a/src/tree_gui.cpp b/src/tree_gui.cpp
--- a/src/tree_gui.cpp
+++ b/src/tree_gui.cpp
@@ -246,6 +246,6 @@ static const WindowDesc _build_trees_des
 
 void ShowBuildTreesToolbar()
 {
-	if (_game_mode != GM_EDITOR && !IsValidCompanyID(_local_company)) return;
+	if (_game_mode != GM_EDITOR && !Company::IsValidID(_local_company)) return;
 	AllocateWindowDescFront<BuildTreesWindow>(&_build_trees_desc, 0);
 }