diff --git a/telethon/events/messagedeleted.py b/telethon/events/messagedeleted.py
index 4116f852..cbbac8cd 100644
--- a/telethon/events/messagedeleted.py
+++ b/telethon/events/messagedeleted.py
@@ -29,5 +29,12 @@ class MessageDeleted(EventBuilder):
             super().__init__(
                 chat_peer=peer, msg_id=(deleted_ids or [0])[0]
             )
+            if peer is None:
+                # If it's not a channel ID, then it was private/small group.
+                # We can't know which one was exactly unless we logged all
+                # messages, but we can indicate that it was maybe either of
+                # both by setting them both to True.
+                self.is_private = self.is_group = True
+
             self.deleted_id = None if not deleted_ids else deleted_ids[0]
             self.deleted_ids = deleted_ids