diff --git a/telethon/errors/rpc_errors_400.py b/telethon/errors/rpc_errors_400.py
index 32591bb5..216910c8 100644
--- a/telethon/errors/rpc_errors_400.py
+++ b/telethon/errors/rpc_errors_400.py
@@ -284,7 +284,7 @@ class UsernameInvalidError(BadRequestError):
     def __init__(self, **kwargs):
         super(Exception, self).__init__(
             self,
-            'Unacceptable username. Must match r"[a-zA-Z][\w\d]{4,32}"'
+            'Unacceptable username. Must match r"[a-zA-Z][\w\d]{4,31}"'
         )