Index: Lib/test/regrtest.py
===================================================================
--- Lib/test/regrtest.py	(revision 85314)
+++ Lib/test/regrtest.py	(working copy)
@@ -252,8 +252,6 @@
     on the command line.
     """
 
-    replace_stdout()
-
     support.record_original_stdout(sys.stdout)
     try:
         opts, args = getopt.getopt(sys.argv[1:], 'hvqxsSrf:lu:t:TD:NLR:FwWM:nj:',
@@ -733,17 +731,6 @@
             tests.append(modname)
     return stdtests + sorted(tests)
 
-def replace_stdout():
-    """Set stdout encoder error handler to backslashreplace (as stderr error
-    handler) to avoid UnicodeEncodeError when printing a traceback"""
-    if os.name == "nt":
-        # Replace sys.stdout breaks the stdout newlines on Windows: issue #8533
-        return
-    stdout = sys.stdout
-    sys.stdout = open(stdout.fileno(), 'w',
-        encoding=stdout.encoding,
-        errors="backslashreplace")
-
 def runtest(test, verbose, quiet,
             testdir=None, huntrleaks=False, debug=False, use_resources=None):
     """Run a single test.
Index: Lib/unittest/runner.py
===================================================================
--- Lib/unittest/runner.py	(revision 85314)
+++ Lib/unittest/runner.py	(working copy)
@@ -2,6 +2,8 @@
 
 import sys
 import time
+import io
+import os
 
 from . import result
 from .signals import registerResult
@@ -12,6 +14,17 @@
 class _WritelnDecorator(object):
     """Used to decorate file-like objects with a handy 'writeln' method"""
     def __init__(self,stream):
+        if stream.errors != "backslashreplace":
+            fd = os.dup(stream.fileno())
+            try:
+                buf = io.open(fd, "wb")
+            except:
+                os.close(fd)
+                raise
+            buf.raw.name = stream.name
+            line_buffering = buf.raw.isatty()
+            stream = io.TextIOWrapper(buf,
+                stream.encoding, "backslashreplace", "\n", line_buffering)
         self.stream = stream
 
     def __getattr__(self, attr):