diff --git a/changelog.d/17570.bugfix b/changelog.d/17570.bugfix
new file mode 100644
index 0000000000..e2964168b1
--- /dev/null
+++ b/changelog.d/17570.bugfix
@@ -0,0 +1 @@
+Fix bug where we would respond with an error when a remote server asked for media that had a length of 0, using the new multipart federation media endpoint.
diff --git a/synapse/media/media_storage.py b/synapse/media/media_storage.py
index cf4208eb71..c25d1a9ba3 100644
--- a/synapse/media/media_storage.py
+++ b/synapse/media/media_storage.py
@@ -544,7 +544,7 @@ def content_length(self) -> Optional[int]:
         Calculate the content length of the multipart response
         in bytes.
         """
-        if not self.length:
+        if self.length is None:
             return None
         # calculate length of json field and content-type, disposition headers
         json_field = json.dumps(self.json_field)