diff --git a/Doc/library/email.message.rst b/Doc/library/email.message.rst
index 58f708c..c3904c7 100644
--- a/Doc/library/email.message.rst
+++ b/Doc/library/email.message.rst
@@ -131,7 +131,11 @@ Here are the methods of the :class:`Message` class:
 
       Return ``True`` if the message's payload is a list of sub-\
       :class:`Message` objects, otherwise return ``False``.  When
-      :meth:`is_multipart` returns ``False``, the payload should be a string object.
+      :meth:`is_multipart` returns ``False``, the payload should be a string
+      object. Although if :meth:`is_multipart` does return ``True``, it does
+      not mean "msg.get_content_maintype() == 'multipart'" will return
+      the same answer. (An example would be when the :class:`Message` is of
+      type ``message/rfc822``)
 
 
    .. method:: set_unixfrom(unixfrom)
@@ -605,6 +609,8 @@ Here are the methods of the :class:`Message` class:
    :class:`Message` objects can also optionally contain two instance attributes,
    which can be used when generating the plain text of a MIME message.
 
+   However this method will not iterate over the subparts of a part whose main-type
+   is not ``multipart`` even though :meth:`is_multipart` returns ``True``.
 
    .. attribute:: preamble