diff --git a/Doc/library/base64.rst b/Doc/library/base64.rst
index 529a7242443820..f9e0e40662ac1b 100644
--- a/Doc/library/base64.rst
+++ b/Doc/library/base64.rst
@@ -74,8 +74,11 @@ POST request.
    of length 2 which specifies the alternative alphabet used instead of the
    ``+`` and ``/`` characters.
 
-   A :exc:`binascii.Error` exception is raised
-   if *s* is incorrectly padded.
+   A :exc:`binascii.Error` exception is raised if *s* contains incorrect padding.
+   When *validate* is ``False`` (the default), extra padding characters and
+   discontinuous padding characters (``=`` characters in the middle of the payload)
+   are silently ignored. When *validate* is ``True``, such incorrect padding
+   will result in a :exc:`binascii.Error`.
 
    If *validate* is ``False`` (the default), characters that are neither
    in the normal base-64 alphabet nor the alternative alphabet are