diff --git a/src/townname_type.h b/src/townname_type.h
index 2dc23567f0..811c8a118c 100644
--- a/src/townname_type.h
+++ b/src/townname_type.h
@@ -16,10 +16,10 @@
 #include "newgrf_townname.h"
 #include "town_type.h"
 #include "string_type.h"
-#include <set>
+#include "3rdparty/cpp-btree/btree_set.h"
 #include <string>
 
-typedef std::set<std::string> TownNames;
+typedef btree::btree_set<std::string> TownNames;
 
 static constexpr uint BUILTIN_TOWNNAME_GENERATOR_COUNT = SPECSTR_TOWNNAME_LAST - SPECSTR_TOWNNAME_START + 1; ///< Number of built-in town name generators.