diff --git a/telethon/events/newmessage.py b/telethon/events/newmessage.py
index 8c1f6625..8bba002a 100644
--- a/telethon/events/newmessage.py
+++ b/telethon/events/newmessage.py
@@ -29,7 +29,7 @@ class NewMessage(EventBuilder):
         if incoming is not None and outgoing is None:
             outgoing = not incoming
         elif outgoing is not None and incoming is None:
-            incoming = not incoming
+            incoming = not outgoing
 
         if incoming and outgoing:
             self.incoming = self.outgoing = None  # Same as no filter