diff --git a/Doc/library/email.encoders.rst b/Doc/library/email.encoders.rst
index 5421b9f66f3..3c32c3bb425 100644
--- a/Doc/library/email.encoders.rst
+++ b/Doc/library/email.encoders.rst
@@ -18,6 +18,10 @@ exactly one argument, the message object to encode.  They usually extract the
 payload, encode it, and reset the payload to this newly encoded value.  They
 should also set the :mailheader:`Content-Transfer-Encoding` header as appropriate.
 
+Note that these functions are not meaningful for a multipart message.  They
+must be applied to individual subparts instead, and will throw a
+:exc:`TypeError` if passed a message whose type is multipart.
+
 Here are the encoding functions provided: