diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 61ed90f39..9ca4d884d 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>