diff --git a/telethon/events/newmessage.py b/telethon/events/newmessage.py
index 7f2d3483..c15b9700 100644
--- a/telethon/events/newmessage.py
+++ b/telethon/events/newmessage.py
@@ -138,9 +138,8 @@ class NewMessage(EventBuilder):
         # Make messages sent to ourselves outgoing unless they're forwarded.
         # This makes it consistent with official client's appearance.
         ori = event.message
-        if isinstance(ori.peer_id, types.PeerUser):
-            if ori.from_id == ori.peer_id and not ori.fwd_from:
-                event.message.out = True
+        if ori.peer_id == types.PeerUser(self_id) and not ori.fwd_from:
+            event.message.out = True
 
         return event