diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 61ed90f39f4fd77c19000d0996b39c4f5d78c93d..9ca4d884ddad9bb123c13525c944011318af95fd 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -34,6 +34,7 @@ class MediaRepositoryResource(Resource):
 
         => POST /_matrix/media/v1/upload HTTP/1.1
            Content-Type: <media-type>
+           Content-Length: <content-length>
 
            <media>