diff --git a/src/pretix/base/services/mail.py b/src/pretix/base/services/mail.py
index b4c9731e5..76a1c5ba6 100644
--- a/src/pretix/base/services/mail.py
+++ b/src/pretix/base/services/mail.py
@@ -143,7 +143,8 @@ def mail(email: str, subject: str, template: Union[str, LazyI18nString],
 def mail_send_task(to: List[str], subject: str, body: str, html: str, sender: str,
                    event: int=None, headers: dict=None) -> bool:
     email = EmailMultiAlternatives(subject, body, sender, to=to, headers=headers)
-    email.attach_alternative(inline_css(html), "text/html")
+    if html is not None:
+        email.attach_alternative(inline_css(html), "text/html")
     if event:
         event = Event.objects.get(id=event)
         backend = event.get_mail_backend()