diff --git a/synapse/rest/media/v1/base_resource.py b/synapse/rest/media/v1/base_resource.py
index 03ebbbefe9..b2aeb8c909 100644
--- a/synapse/rest/media/v1/base_resource.py
+++ b/synapse/rest/media/v1/base_resource.py
@@ -155,9 +155,9 @@ class BaseMediaResource(Resource):
 
                 # If there isn't check for an ascii name.
                 if not upload_name:
-                    upload_name = params.get("filename", None)
-                    if upload_name and not is_ascii(upload_name):
-                        upload_name = None
+                    upload_name_ascii = params.get("filename", None)
+                    if upload_name_ascii and is_ascii(upload_name_ascii):
+                        upload_name = upload_name_ascii
 
                 if upload_name:
                     upload_name = urlparse.unquote(upload_name)