diff --git a/telegram/base.py b/telegram/base.py
index 80259ac8740..c921b3225da 100644
--- a/telegram/base.py
+++ b/telegram/base.py
@@ -65,7 +65,8 @@ def to_dict(self):
                        '_credentials',
                        '_decrypted_credentials',
                        '_decrypted_data',
-                       '_decrypted_secret'):
+                       '_decrypted_secret',
+                       '_effective_attachment'):
                 continue
 
             value = self.__dict__[key]