diff --git a/src/snek/view/channel.py b/src/snek/view/channel.py
index fd37cad..82675f0 100644
--- a/src/snek/view/channel.py
+++ b/src/snek/view/channel.py
@@ -114,7 +114,7 @@ class ChannelAttachmentView(BaseView):
             response.headers["Content-Disposition"] = (
                 f'attachment; filename="{channel_attachment["name"]}"'
             )
-            response.headers["Content-Type"] = original_format
+            response.headers["Content-Type"] = original_format or "application/octet-stream"
             return response
 
     async def post(self):