diff --git a/src/sponsors/email.py b/src/sponsors/email.py
index e8cfece8..685c1630 100644
--- a/src/sponsors/email.py
+++ b/src/sponsors/email.py
@@ -27,7 +27,7 @@ def add_sponsorticket_email(ticket):
             to_recipients=ticket.sponsor.ticket_email,
             formatdict=formatdict,
             subject=subject,
-            attachment=f,
+            attachment=f.read(),
             attachment_filename=filename,
         )