Index: build/run_tests.py
===================================================================
--- build/run_tests.py	(revision 1876712)
+++ build/run_tests.py	(working copy)
@@ -48,6 +48,7 @@
 '''
 
 import os, sys, shutil, codecs
+import io
 import re
 import logging
 import optparse, subprocess, threading, traceback
@@ -844,6 +845,12 @@
 
     # setup the output pipes
     if self.log:
+      need_stdout_reconstruct = (    isinstance(sys.stdout, io.IOBase)
+                                 and not isinstance(sys.stdout.buffer.raw,
+                                                    io.FileIO))
+      need_stderr_reconstruct = (    isinstance(sys.stderr, io.IOBase)
+                                 and not isinstance(sys.stderr.buffer.raw,
+                                                    io.FileIO))
       sys.stdout.flush()
       sys.stderr.flush()
       self.log.flush()
@@ -851,6 +858,12 @@
       old_stderr = os.dup(sys.stderr.fileno())
       os.dup2(self.log.fileno(), sys.stdout.fileno())
       os.dup2(self.log.fileno(), sys.stderr.fileno())
+      if need_stdout_reconstruct:
+        sys.stdout = open(sys.stdout.fileno(), 'w', encoding='utf-8',
+                          errors='replace', closefd=False)
+      if need_stderr_reconstruct:
+        sys.stderr = open(sys.stderr.fileno(), 'w', encoding='utf-8',
+                          errors='replace', closefd=False)
 
     # These have to be class-scoped for use in the progress_func()
     self.dots_written = 0
@@ -897,6 +910,12 @@
       os.dup2(old_stderr, sys.stderr.fileno())
       os.close(old_stdout)
       os.close(old_stderr)
+      if need_stdout_reconstruct:
+        sys.stdout = open(sys.stdout.fileno(), 'w', encoding='utf-8',
+                          errors='replace', closefd=False)
+      if need_stderr_reconstruct:
+        sys.stderr = open(sys.stderr.fileno(), 'w', encoding='utf-8',
+                          errors='replace', closefd=False)
 
     return failed