diff -r 09d4d47ad210 Modules/_io/fileio.c
--- a/Modules/_io/fileio.c	Tue Jan 31 13:53:39 2017 +0100
+++ b/Modules/_io/fileio.c	Wed Feb 01 03:07:22 2017 +0000
@@ -230,12 +230,13 @@
                          int closefd, PyObject *opener)
 /*[clinic end generated code: output=23413f68e6484bbd input=193164e293d6c097]*/
 {
+#ifdef MS_WINDOWS
+    Py_UNICODE *widename = NULL;
+#else
     const char *name = NULL;
+#endif
     PyObject *stringobj = NULL;
     const char *s;
-#ifdef MS_WINDOWS
-    Py_UNICODE *widename = NULL;
-#endif
     int ret = 0;
     int rwa = 0, plus = 0;
     int flags = 0;
@@ -277,24 +278,21 @@
         PyErr_Clear();
     }
 
+    if (fd < 0) {
 #ifdef MS_WINDOWS
-    if (PyUnicode_Check(nameobj)) {
         Py_ssize_t length;
-        widename = PyUnicode_AsUnicodeAndSize(nameobj, &length);
+        if (!PyUnicode_FSDecoder(nameobj, &stringobj)) {
+            return -1;
+        }
+        widename = PyUnicode_AsUnicodeAndSize(stringobj, &length);
         if (widename == NULL)
             return -1;
-        if (wcslen(widename) != length) {
-            PyErr_SetString(PyExc_ValueError, "embedded null character");
-            return -1;
-        }
-    } else
-#endif
-    if (fd < 0)
-    {
+#else
         if (!PyUnicode_FSConverter(nameobj, &stringobj)) {
             return -1;
         }
         name = PyBytes_AS_STRING(stringobj);
+#endif
     }
 
     s = mode;
@@ -386,11 +384,10 @@
             do {
                 Py_BEGIN_ALLOW_THREADS
 #ifdef MS_WINDOWS
-                if (widename != NULL)
                     self->fd = _wopen(widename, flags, 0666);
-                else
+#else
+                    self->fd = open(name, flags, 0666);
 #endif
-                    self->fd = open(name, flags, 0666);
                 Py_END_ALLOW_THREADS
             } while (self->fd < 0 && errno == EINTR &&
                      !(async_err = PyErr_CheckSignals()));