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):