diff --git a/telethon/client/auth.py b/telethon/client/auth.py
index 8592b1ef..52d671ac 100644
--- a/telethon/client/auth.py
+++ b/telethon/client/auth.py
@@ -19,8 +19,8 @@ class AuthMethods:
 
     def start(
             self: 'TelegramClient',
-            phone: typing.Callable[[], str] | str = lambda: input('Please enter your phone (or bot token): '),
-            password: typing.Callable[[], str] | str = lambda: getpass.getpass('Please enter your password: '),
+            phone: typing.Union[typing.Callable[[], str], str] = lambda: input('Please enter your phone (or bot token): '),
+            password: typing.Union[typing.Callable[[], str], str] = lambda: getpass.getpass('Please enter your password: '),
             *,
             bot_token: str = None,
             force_sms: bool = False,