Index: Doc/library/base64.rst
===================================================================
--- Doc/library/base64.rst	(revision 74261)
+++ Doc/library/base64.rst	(working copy)
@@ -43,9 +43,9 @@
    length 2 (additional characters are ignored) which specifies the alternative
    alphabet used instead of the ``+`` and ``/`` characters.
 
-   The decoded string is returned.  A :exc:`TypeError` is raised if *s* were
-   incorrectly padded or if there are non-alphabet characters present in the
-   string.
+   The decoded string is returned.  A :exc:`TypeError` is raised if *s* is
+   incorrectly padded. Non-base64-alphabet characters are discarded prior to the
+   padding check, per RFC 2045 and allowances in RFC 3548.
 
 
 .. function:: standard_b64encode(s)