diff --git a/telethon/client/updates.py b/telethon/client/updates.py
index 2a9dee95..0f1a1cc3 100644
--- a/telethon/client/updates.py
+++ b/telethon/client/updates.py
@@ -459,10 +459,10 @@ class UpdateMethods:
 
             if not pts_date:
                 # First-time, can't get difference. Get pts instead.
-                result = await self(functions.messages.GetPeerDialogsRequest([
-                    utils.get_input_dialog(where)
-                ]))
-                self._state_cache[channel_id] = result.dialogs[0].pts
+                result = await self(functions.channels.getFullChannel(
+                    channel=where
+                ))
+                self._state_cache[channel_id] = result.full_chat.pts
                 return
 
             result = await self(functions.updates.GetChannelDifferenceRequest(