diff -r 43ae2a243eca Lib/test/test_genericpath.py
--- a/Lib/test/test_genericpath.py	Thu Jul 26 00:47:15 2012 +0200
+++ b/Lib/test/test_genericpath.py	Thu Jul 26 12:51:23 2012 +0200
@@ -299,8 +299,7 @@ class CommonTest(GenericTest):
 
         unicwd = '\xe7w\xf0'
         try:
-            fsencoding = support.TESTFN_ENCODING or "ascii"
-            unicwd.encode(fsencoding)
+            os.fsencode(unicwd)
         except (AttributeError, UnicodeEncodeError):
             # FS encoding is probably ASCII
             pass
@@ -312,10 +311,19 @@ class CommonTest(GenericTest):
     @unittest.skipIf(sys.platform == 'darwin',
         "Mac OS X denies the creation of a directory with an invalid utf8 name")
     def test_nonascii_abspath(self):
+        name = b'\xe7w\xf0'
+        if sys.platform == 'win32':
+            try:
+                os.fsdecode(name)
+            except UnicodeDecodeError:
+                self.skipTest("the filename %a is not decodable "
+                              "from the ANSI code page %s"
+                              % (name, sys.getfilesystemencoding()))
+
         # Test non-ASCII, non-UTF8 bytes in the path.
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", DeprecationWarning)
-            with support.temp_cwd(b'\xe7w\xf0'):
+            with support.temp_cwd(name):
                 self.test_abspath()
 
 
diff -r 43ae2a243eca Modules/posixmodule.c
--- a/Modules/posixmodule.c	Thu Jul 26 00:47:15 2012 +0200
+++ b/Modules/posixmodule.c	Thu Jul 26 12:51:23 2012 +0200
@@ -1129,20 +1129,15 @@ win32_error_object(char* function, PyObj
 static PyObject *
 path_posix_error(char *function_name, path_t *path)
 {
-    if (path->narrow)
-        return posix_error_with_filename(path->narrow);
-    return posix_error();
+    return PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, path->object);
 }
 
 static PyObject *
 path_error(char *function_name, path_t *path)
 {
 #ifdef MS_WINDOWS
-    if (path->narrow)
-        return win32_error(function_name, path->narrow);
-    if (path->wide)
-        return win32_error_unicode(function_name, path->wide);
-    return win32_error(function_name, NULL);
+    return PyErr_SetExcFromWindowsErrWithFilenameObject(PyExc_OSError,
+                                                        0, path->object);
 #else
     return path_posix_error(function_name, path);
 #endif
diff -r 43ae2a243eca Python/errors.c
--- a/Python/errors.c	Thu Jul 26 00:47:15 2012 +0200
+++ b/Python/errors.c	Thu Jul 26 12:51:23 2012 +0200
@@ -463,11 +463,24 @@ PyErr_SetFromErrnoWithFilenameObject(PyO
     return NULL;
 }
 
+static PyObject *
+decode_filename(const char *filename)
+{
+    PyObject *obj;
+    if (!filename)
+        return NULL;
+    obj = PyUnicode_DecodeFSDefault(filename);
+    if (obj == NULL) {
+        PyErr_Clear();
+        obj = PyBytes_FromString(filename);
+    }
+    return obj;
+}
 
 PyObject *
 PyErr_SetFromErrnoWithFilename(PyObject *exc, const char *filename)
 {
-    PyObject *name = filename ? PyUnicode_DecodeFSDefault(filename) : NULL;
+    PyObject *name = decode_filename(filename);
     PyObject *result = PyErr_SetFromErrnoWithFilenameObject(exc, name);
     Py_XDECREF(name);
     return result;
@@ -558,7 +571,7 @@ PyObject *PyErr_SetExcFromWindowsErrWith
     int ierr,
     const char *filename)
 {
-    PyObject *name = filename ? PyUnicode_DecodeFSDefault(filename) : NULL;
+    PyObject *name = decode_filename(filename);
     PyObject *ret = PyErr_SetExcFromWindowsErrWithFilenameObject(exc,
                                                                  ierr,
                                                                  name);
@@ -595,7 +608,7 @@ PyObject *PyErr_SetFromWindowsErrWithFil
     int ierr,
     const char *filename)
 {
-    PyObject *name = filename ? PyUnicode_DecodeFSDefault(filename) : NULL;
+    PyObject *name = decode_filename(filename);
     PyObject *result = PyErr_SetExcFromWindowsErrWithFilenameObject(
                                                   PyExc_WindowsError,
                                                   ierr, name);
@@ -892,7 +905,7 @@ PyErr_SyntaxLocationEx(const char *filen
         }
     }
     if (filename != NULL) {
-        tmp = PyUnicode_DecodeFSDefault(filename);
+        tmp = decode_filename(filename);
         if (tmp == NULL)
             PyErr_Clear();
         else {