diff --git a/telethon/tl/custom/message.py b/telethon/tl/custom/message.py
index 02cd1448..58015e46 100644
--- a/telethon/tl/custom/message.py
+++ b/telethon/tl/custom/message.py
@@ -19,6 +19,7 @@ class Message:
             in the original :tl:`Message`.
     """
     def __init__(self, client, original, entities, input_chat):
+        self.__dict__['_init'] = False
         self.original_message = original
         self.stringify = self.original_message.stringify
         self.to_dict = self.original_message.to_dict
@@ -42,6 +43,7 @@ class Message:
             elif fwd.channel_id:
                 self._fwd_from_entity = entities.get(get_peer_id(
                     types.PeerChannel(fwd.channel_id)))
+        self._init = True
 
     def __new__(cls, client, original, entities, input_chat):
         if isinstance(original, types.Message):
@@ -55,7 +57,10 @@ class Message:
         return getattr(self.original_message, item)
 
     def __setattr__(self, name, value):
-        return setattr(self.original_message, name, value)
+        if not self._init or name in self.__dict__:
+            self.__dict__[name] = value
+        else:
+            setattr(self.original_message, name, value)
 
     def __str__(self):
         return str(self.original_message)