diff --git a/mautrix_telegram/portal/portal_telegram.py b/mautrix_telegram/portal/portal_telegram.py
index d43b873a..698a66ef 100644
--- a/mautrix_telegram/portal/portal_telegram.py
+++ b/mautrix_telegram/portal/portal_telegram.py
@@ -104,7 +104,7 @@ class PortalTelegram(BasePortal, ABC):
         name = f"image{sane_mimetypes.guess_extension(file.mime_type)}"
         await intent.set_typing(self.mxid, is_typing=False)
         content = MediaMessageEventContent(uri=file.mxc, info=info, body=name, relates_to=relates_to,
-                                           external_url=self.get_external_url(evt))
+                                           external_url=self._get_external_url(evt))
         result = await intent.send_message(self.mxid, content, timestamp=evt.date)
         if evt.message:
             caption_content = await formatter.telegram_to_matrix(evt, source, self.main_intent,