diff --git a/endpoints/web.py b/endpoints/web.py
index 05fe65847..4717f7d40 100644
--- a/endpoints/web.py
+++ b/endpoints/web.py
@@ -191,7 +191,7 @@ def render_avatar(avatar_hash, headers):
   except ValueError:
     size = 16
 
-  generated = Avatar.generate(size, avatar_hash)
+  generated = Avatar.generate(size, avatar_hash, "PNG")
   resp = make_response(generated, 200, {'Content-Type': 'image/png'})
   resp.headers.extend(headers)
   return resp