diff --git a/src/group.h b/src/group.h
--- a/src/group.h
+++ b/src/group.h
@@ -113,6 +113,4 @@ void RemoveVehicleFromGroup(const Vehicl
 void RemoveAllGroupsForCompany(const CompanyID company);
 bool GroupIsInGroup(GroupID search, GroupID group);
 
-extern GroupID _new_group_id;
-
 #endif /* GROUP_H */