diff --git a/cgi-bin/form.py b/cgi-bin/form.py
index f0da423..ddb8694 100755
--- a/cgi-bin/form.py
+++ b/cgi-bin/form.py
@@ -165,7 +165,7 @@ match request_uri:
 		ticket_details["Adresse"] = get_form_value("addressline")
 		ticket_details["PLZ"] = get_form_value("postalcode")
 		ticket_details["Stadt"] = get_form_value("city")
-		attachment = get_form_value("document")
+		attachment = get_form_value("document", cast=bytes)
 
 		# Note: the actual form contains a checkbox for whether the user has
 		# read the guidelines, but we don't actually bother checking that here.