diff --git a/starlette/testclient.py b/starlette/testclient.py
index d8fc20b46..5811c6e39 100644
--- a/starlette/testclient.py
+++ b/starlette/testclient.py
@@ -691,7 +691,7 @@ def reset_portal() -> None:
                 self.portal = None
 
             send1, receive1 = anyio.create_memory_object_stream[
-                typing.Optional[typing.MutableMapping[str, typing.Any]]
+                typing.Union[typing.MutableMapping[str, typing.Any], None]
             ](math.inf)
             send2, receive2 = anyio.create_memory_object_stream[typing.MutableMapping[str, typing.Any]](math.inf)
             for channel in (send1, send2, receive1, receive2):