diff --git a/telethon/errors/__init__.py b/telethon/errors/__init__.py
index ca07f6c0..7bb56af8 100644
--- a/telethon/errors/__init__.py
+++ b/telethon/errors/__init__.py
@@ -3,7 +3,7 @@ import re
 
 from .common import (
     ReadCancelledError, InvalidParameterError, TypeNotFoundError,
-    InvalidChecksumError, CdnFileTamperedError
+    InvalidChecksumError, BrokenAuthKeyError, CdnFileTamperedError
 )
 
 from .rpc_errors import (
diff --git a/telethon/errors/common.py b/telethon/errors/common.py
index fc0a8e5f..49742da4 100644
--- a/telethon/errors/common.py
+++ b/telethon/errors/common.py
@@ -38,6 +38,14 @@ class InvalidChecksumError(Exception):
         self.valid_checksum = valid_checksum
 
 
+class BrokenAuthKeyError(Exception):
+    def __init__(self):
+        super().__init__(
+            self,
+            'The authorization key is broken, and it must be reset.'
+        )
+
+
 class CdnFileTamperedError(Exception):
     def __init__(self):
         super().__init__(
diff --git a/telethon/network/mtproto_plain_sender.py b/telethon/network/mtproto_plain_sender.py
index 77600abd..5ced50a9 100644
--- a/telethon/network/mtproto_plain_sender.py
+++ b/telethon/network/mtproto_plain_sender.py
@@ -1,5 +1,6 @@
 import time
 
+from ..errors import BrokenAuthKeyError
 from ..extensions import BinaryReader, BinaryWriter
 
 
@@ -36,6 +37,10 @@ class MtProtoPlainSender:
     def receive(self):
         """Receives a plain packet, returning the body of the response"""
         body = self._connection.recv()
+        if body == b'l\xfe\xff\xff':  # -404 little endian signed
+            # Broken authorization, must reset the auth key
+            raise BrokenAuthKeyError()
+
         with BinaryReader(body) as reader:
             reader.read_long()  # auth_key_id
             reader.read_long()  # msg_id
diff --git a/telethon/telegram_bare_client.py b/telethon/telegram_bare_client.py
index 0990fa27..f4ecf490 100644
--- a/telethon/telegram_bare_client.py
+++ b/telethon/telegram_bare_client.py
@@ -7,13 +7,14 @@ from os import path
 from . import helpers as utils
 from .crypto import rsa, CdnDecrypter
 from .errors import (
-    RPCError, FloodWaitError, FileMigrateError, TypeNotFoundError
+    RPCError, BrokenAuthKeyError,
+    FloodWaitError, FileMigrateError, TypeNotFoundError
 )
 from .network import authenticator, MtProtoSender, Connection, ConnectionMode
 from .tl import TLObject, Session
 from .tl.all_tlobjects import LAYER
 from .tl.functions import (
-    InitConnectionRequest, InvokeWithLayerRequest, PingRequest
+    InitConnectionRequest, InvokeWithLayerRequest
 )
 from .tl.functions.auth import (
     ImportAuthorizationRequest, ExportAuthorizationRequest
@@ -115,8 +116,11 @@ class TelegramBareClient:
             if not self.session.auth_key:
                 # New key, we need to tell the server we're going to use
                 # the latest layer
-                self.session.auth_key, self.session.time_offset = \
-                    authenticator.do_authentication(connection)
+                try:
+                    self.session.auth_key, self.session.time_offset = \
+                        authenticator.do_authentication(connection)
+                except BrokenAuthKeyError:
+                    return False
 
                 self.session.layer = LAYER
                 self.session.save()