diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index f39f8b0..d5b03ee 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -253,34 +253,23 @@
     }
 
 #ifdef MS_WINDOWS
-    if (PyUnicode_Check(nameobj))
+    if (PyUnicode_Check(nameobj)) {
+        int rv = _PyUnicode_HasNULChars(nameobj);
+        if (rv) {
+            if (rv != -1)
+                PyErr_SetString(PyExc_TypeError, "embedded NUL character");
+            return -1;
+        }
         widename = PyUnicode_AS_UNICODE(nameobj);
+    }
     if (widename == NULL)
 #endif
     if (fd < 0)
     {
-        if (PyBytes_Check(nameobj) || PyByteArray_Check(nameobj)) {
-            Py_ssize_t namelen;
-            if (PyObject_AsCharBuffer(nameobj, &name, &namelen) < 0)
-                return -1;
+        if (!PyUnicode_FSConverter(nameobj, &stringobj)) {
+            return -1;
         }
-        else {
-            PyObject *u = PyUnicode_FromObject(nameobj);
-
-            if (u == NULL)
-                return -1;
-
-            stringobj = PyUnicode_EncodeFSDefault(u);
-            Py_DECREF(u);
-            if (stringobj == NULL)
-                return -1;
-            if (!PyBytes_Check(stringobj)) {
-                PyErr_SetString(PyExc_TypeError,
-                                "encoder failed to return bytes");
-                goto error;
-            }
-            name = PyBytes_AS_STRING(stringobj);
-        }
+        name = PyBytes_AS_STRING(stringobj);
     }
 
     s = mode;