1 files changed, 6 insertions, 0 deletions
diff --git a/Lib/email/mime/multipart.py b/Lib/email/mime/multipart.py
index 5c8c9db..9661865 100644
--- a/Lib/email/mime/multipart.py
+++ b/Lib/email/mime/multipart.py
@@ -34,6 +34,12 @@ class MIMEMultipart(MIMEBase):
         keyword arguments (or passed into the _params argument).
         """
         MIMEBase.__init__(self, 'multipart', _subtype, **_params)
+
+        # Initialise _payload to an empty list as the Message superclass's
+        # implementation of is_multipart assumes that _payload is a list for
+        # multipart messages.
+        self._payload = []
+
         if _subparts:
             for p in _subparts:
                 self.attach(p)