diff --git a/Doc/library/io.rst b/Doc/library/io.rst
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -754,7 +754,8 @@
    It inherits :class:`TextIOBase`.
 
    *encoding* gives the name of the encoding that the stream will be decoded or
-   encoded with.  It defaults to ``locale.getpreferredencoding(False)``.
+   encoded with.  It defaults to
+   :func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`.
 
    *errors* is an optional string that specifies how encoding and decoding
    errors are to be handled.  Pass ``'strict'`` to raise a :exc:`ValueError`
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -287,7 +287,8 @@
 
    If *universal_newlines* is ``True``, the file objects *stdin*, *stdout*
    and *stderr* will be opened as text files with universal newlines support,
-   using the encoding returned by :func:`locale.getpreferredencoding`.
+   using the encoding returned by
+   :func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`.
    For *stdin*, line ending characters ``'\n'`` in the input will be converted
    to the default line separator :data:`os.linesep`.  For *stdout* and
    *stderr*, all line endings in the output will be converted to ``'\n'``.
@@ -308,6 +309,12 @@
    access to other shell features such as filename wildcards, shell pipes and
    environment variable expansion.
 
+   .. versionchanged:: 3.3
+      When *universal_newlines* is ``True``, the class uses the encoding
+      :func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`
+      instead of ``locale.getpreferredencoding()``.  See the
+      :class:`io.TextIOWrapper` class for more information on this change.
+
    .. warning::
 
       Executing shell commands that incorporate unsanitized input from an