diff --git a/boards/models/post/sync.py b/boards/models/post/sync.py
--- a/boards/models/post/sync.py
+++ b/boards/models/post/sync.py
@@ -320,4 +320,4 @@ class SyncManager:
         if tag_refs is not None:
             attachment_ref = et.SubElement(tag_refs, TAG_ATTACHMENT_REF)
             attachment_ref.set(ATTR_REF, attachment.hash)
-            attachment_ref.set(ATTR_URL, attachment.url)
+            attachment_ref.set(ATTR_URL, attachment.file.url)