diff --git a/ordered_set/__init__.py b/ordered_set/__init__.py
index ccd1cbf..72caedd 100644
--- a/ordered_set/__init__.py
+++ b/ordered_set/__init__.py
@@ -365,8 +365,7 @@ def union(self, *sets: SetLike[T]) -> "OrderedSet[T]":
         cls: type = OrderedSet
         if isinstance(self, OrderedSet):
             cls = self.__class__
-        containers = map(list, it.chain([self], sets))
-        items = it.chain.from_iterable(containers)
+        items = itertools.chain(self, *sets)
         return cls(items)
 
     def __and__(self, other: SetLike[T]) -> "OrderedSet[T]":