diff -r 523cfc78847c Lib/lib2to3/fixes/fix_bytesliterals.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/lib2to3/fixes/fix_bytesliterals.py	Sun Sep 08 03:03:12 2013 +0300
@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+"""Fixer for non-ascii bytes literals.
+
+"""
+# Author: Serhiy Storchaka
+
+# Local imports
+from ..pgen2 import token
+from .. import fixer_base
+from ..fixer_util import String
+
+class FixBytesliterals(fixer_base.BaseFix):
+    # This is so simple that we don't need the pattern compiler.
+
+    _accept_type = token.STRING
+
+    def match(self, node):
+        # Override
+        return node.value[0] in u'bB'
+
+    def start_tree(self, tree, filename):
+        super(FixBytesliterals, self).start_tree(tree, filename)
+        self.encoding = tree.encoding or 'ascii'
+
+    def transform(self, node, results):
+        val = node.value
+        print 'transform', val
+        try:
+            val.encode('ascii')
+        except UnicodeEncodeError:
+            self.warning(node, 'Value of bytes literal is encoding dependend')
+            if val[1] in 'rR':
+                assert val[0] in u'bB'
+                val = val[:1] + val[2:]
+                val = val.replace(u'\\', ur'\\')
+            val = val.encode(self.encoding).decode('latin1')
+            val = val.encode('ascii', 'backslashreplace').decode('ascii')
+        if val == node.value:
+            return node
+        new = node.clone()
+        new.value = val
+        return new
diff -r 523cfc78847c Lib/lib2to3/refactor.py
--- a/Lib/lib2to3/refactor.py	Sat Sep 07 15:23:36 2013 +0300
+++ b/Lib/lib2to3/refactor.py	Sun Sep 08 03:03:12 2013 +0300
@@ -345,13 +345,13 @@
         input += u"\n" # Silence certain parse errors
         if doctests_only:
             self.log_debug("Refactoring doctests in %s", filename)
-            output = self.refactor_docstring(input, filename)
+            output = self.refactor_docstring(input, filename, encoding)
             if self.write_unchanged_files or output != input:
                 self.processed_file(output, filename, input, write, encoding)
             else:
                 self.log_debug("No doctest changes in %s", filename)
         else:
-            tree = self.refactor_string(input, filename)
+            tree = self.refactor_string(input, filename, encoding)
             if self.write_unchanged_files or (tree and tree.was_changed):
                 # The [:-1] is to take off the \n we added earlier
                 self.processed_file(unicode(tree)[:-1], filename,
@@ -359,7 +359,7 @@
             else:
                 self.log_debug("No changes in %s", filename)
 
-    def refactor_string(self, data, name):
+    def refactor_string(self, data, name, encoding=None):
         """Refactor a given input string.
 
         Args:
@@ -381,6 +381,7 @@
             return
         finally:
             self.driver.grammar = self.grammar
+        tree.encoding = encoding
         tree.future_features = features
         self.log_debug("Refactoring %s", name)
         self.refactor_tree(tree, name)
@@ -549,7 +550,7 @@
     PS1 = ">>> "
     PS2 = "... "
 
-    def refactor_docstring(self, input, filename):
+    def refactor_docstring(self, input, filename, encoding=None):
         """Refactors a docstring, looking for doctests.
 
         This returns a modified version of the input string.  It looks
@@ -592,7 +593,7 @@
                                                 indent, filename))
         return u"".join(result)
 
-    def refactor_doctest(self, block, lineno, indent, filename):
+    def refactor_doctest(self, block, lineno, indent, filename, encoding=None):
         """Refactors one doctest.
 
         A doctest is given as a block of lines, the first of which starts
@@ -609,6 +610,7 @@
             self.log_error("Can't parse docstring in %s line %s: %s: %s",
                            filename, lineno, err.__class__.__name__, err)
             return block
+        tree.encoding = encoding
         if self.refactor_tree(tree, filename):
             new = unicode(tree).splitlines(True)
             # Undo the adjustment of the line numbers in wrap_toks() below.