diff --git a/telethon/network/mtprotosender.py b/telethon/network/mtprotosender.py
index 17c5e2e5..556d0a7f 100644
--- a/telethon/network/mtprotosender.py
+++ b/telethon/network/mtprotosender.py
@@ -369,6 +369,16 @@ class MTProtoSender:
                 self._log.info('Failed reconnection attempt %d with %s',
                                attempt, e.__class__.__name__)
                 await asyncio.sleep(self._delay)
+            except BufferError as e:
+                # TODO there should probably only be one place to except all these errors
+                if isinstance(e, InvalidBufferError) and e.code == 404:
+                    self._log.info('Broken authorization key; resetting')
+                else:
+                    self._log.warning('Invalid buffer %s', e)
+
+                self.auth_key.key = None
+                if self._auth_key_callback:
+                    self._auth_key_callback(None)
             except Exception as e:
                 last_error = e
                 self._log.exception('Unexpected exception reconnecting on '