diff --git a/server.py b/server.py
index 8d7d8d1..3a70420 100644
--- a/server.py
+++ b/server.py
@@ -206,6 +206,8 @@ def preview_url(
                     )
                     if upload_response:
                         og_tags[tag_name] = upload_response
+                        if tag_name == "image":
+                            og_tags["matrix:image:size"] = len(response_media.content)
                         logging.info("Uploaded media: %r" % _url)
                     else:
                         logging.warning("Failed to upload media: %r (no returned mxc)", _url)