diff --git a/telethon/tl/custom/conversation.py b/telethon/tl/custom/conversation.py
index eeadd108..99fff7da 100644
--- a/telethon/tl/custom/conversation.py
+++ b/telethon/tl/custom/conversation.py
@@ -372,7 +372,7 @@ class Conversation(ChatGetter):
             else:
                 pending.cancel()
 
-        for _, fut in self._custom:
+        for _, fut in self._custom.values():
             if exception:
                 fut.set_exception(exception)
             else: