diff -r 86ddd32068a1 Modules/posixmodule.c
--- a/Modules/posixmodule.c	Tue Jan 03 11:20:15 2017 +0200
+++ b/Modules/posixmodule.c	Fri Jan 06 00:08:31 2017 +0800
@@ -785,7 +785,9 @@
  *     The length of the path in characters, if specified as
  *     a string.
  *   path.object
- *     The original object passed in.
+ *     The original object passed in (if get a PathLike object,
+ *     the result of PyOS_FSPath() is treated as the original object).
+ *     Own a reference to the object.
  *   path.cleanup
  *     For internal use only.  May point to a temporary object.
  *     (Pay no attention to the man behind the curtain.)
@@ -837,23 +839,22 @@
 
 static void
 path_cleanup(path_t *path) {
-    if (path->cleanup) {
-        Py_CLEAR(path->cleanup);
-    }
+    Py_CLEAR(path->object);
+    Py_CLEAR(path->cleanup);
 }
 
 static int
 path_converter(PyObject *o, void *p)
 {
     path_t *path = (path_t *)p;
-    PyObject *bytes, *to_cleanup = NULL;
+    PyObject *bytes = NULL;
     Py_ssize_t length;
     int is_index, is_buffer, is_bytes, is_unicode;
-    /* Default to failure, forcing explicit signaling of succcess. */
+    /* Default to failure, forcing explicit signaling of success. */
     int ret = 0;
     const char *narrow;
 #ifdef MS_WINDOWS
-    PyObject *wo;
+    PyObject *wo = NULL;
     const wchar_t *wide;
 #endif
 
@@ -870,7 +871,9 @@
     }
 
     /* Ensure it's always safe to call path_cleanup(). */
-    path->cleanup = NULL;
+    path->object = path->cleanup = NULL;
+    /* path->object owns a reference to the original object */
+    Py_INCREF(o);
 
     if ((o == Py_None) && path->nullable) {
         path->wide = NULL;
@@ -899,13 +902,13 @@
 
         func = _PyObject_LookupSpecial(o, &PyId___fspath__);
         if (NULL == func) {
-            goto error_exit;
-        }
-
-        o = to_cleanup = _PyObject_CallNoArg(func);
+            goto error_format;
+        }
+        /* still owns a reference to the original object */
+        Py_SETREF(o, _PyObject_CallNoArg(func));
         Py_DECREF(func);
         if (NULL == o) {
-            goto error_exit;
+            goto error_format;
         }
         else if (PyUnicode_Check(o)) {
             is_unicode = 1;
@@ -914,7 +917,7 @@
             is_bytes = 1;
         }
         else {
-            goto error_exit;
+            goto error_format;
         }
     }
 
@@ -922,26 +925,27 @@
 #ifdef MS_WINDOWS
         wide = PyUnicode_AsUnicodeAndSize(o, &length);
         if (!wide) {
-            goto exit;
+            goto error_exit;
         }
         if (length > 32767) {
             FORMAT_EXCEPTION(PyExc_ValueError, "%s too long for Windows");
-            goto exit;
+            goto error_exit;
         }
         if (wcslen(wide) != length) {
             FORMAT_EXCEPTION(PyExc_ValueError, "embedded null character in %s");
-            goto exit;
+            goto error_exit;
         }
 
         path->wide = wide;
+        path->narrow = False;
         path->length = length;
         path->object = o;
         path->fd = -1;
         ret = 1;
-        goto exit;
+        goto success_exit;
 #else
         if (!PyUnicode_FSConverter(o, &bytes)) {
-            goto exit;
+            goto error_exit;
         }
 #endif
     }
@@ -961,16 +965,16 @@
             path->nullable ? "string, bytes, os.PathLike or None" :
                              "string, bytes or os.PathLike",
             Py_TYPE(o)->tp_name)) {
-            goto exit;
+            goto error_exit;
         }
         bytes = PyBytes_FromObject(o);
         if (!bytes) {
-            goto exit;
+            goto error_exit;
         }
     }
     else if (is_index) {
         if (!_fd_converter(o, &path->fd)) {
-            goto exit;
+            goto error_exit;
         }
         path->wide = NULL;
 #ifdef MS_WINDOWS
@@ -981,10 +985,10 @@
         path->length = 0;
         path->object = o;
         ret = 1;
-        goto exit;
+        goto success_exit;
     }
     else {
- error_exit:
+ error_format:
         PyErr_Format(PyExc_TypeError, "%s%s%s should be %s, not %.200s",
             path->function_name ? path->function_name : "",
             path->function_name ? ": "                : "",
@@ -995,15 +999,14 @@
             path->nullable ? "string, bytes, os.PathLike or None" :
                              "string, bytes or os.PathLike",
             Py_TYPE(o)->tp_name);
-        goto exit;
+        goto error_exit;
     }
 
     length = PyBytes_GET_SIZE(bytes);
     narrow = PyBytes_AS_STRING(bytes);
     if ((size_t)length != strlen(narrow)) {
         FORMAT_EXCEPTION(PyExc_ValueError, "embedded null character in %s");
-        Py_DECREF(bytes);
-        goto exit;
+        goto error_exit;
     }
 
 #ifdef MS_WINDOWS
@@ -1012,42 +1015,51 @@
         length
     );
     if (!wo) {
-        goto exit;
-    }
-
-    wide = PyUnicode_AsWideCharString(wo, &length);
-    Py_DECREF(wo);
-
+        goto error_exit;
+    }
+
+    wide = PyUnicode_AsUnicodeAndSize(wo, &length);
     if (!wide) {
-        goto exit;
+        goto error_exit;
     }
     if (length > 32767) {
         FORMAT_EXCEPTION(PyExc_ValueError, "%s too long for Windows");
-        goto exit;
+        goto error_exit;
     }
     if (wcslen(wide) != length) {
         FORMAT_EXCEPTION(PyExc_ValueError, "embedded null character in %s");
-        goto exit;
+        goto error_exit;
     }
     path->wide = wide;
     path->narrow = TRUE;
+    path->cleanup = wo;
+    ret = Py_CLEANUP_SUPPORTED;
+    Py_DECREF(bytes);
 #else
     path->wide = NULL;
     path->narrow = narrow;
+    if (bytes == o) {
+        /* Still a reference owned by path->object, don't have to
+           worry about path->narrow is used after free. */
+        Py_DECREF(bytes);
+        ret = 1;
+    }
+    else {
+        path->cleanup = bytes;
+        ret = Py_CLEANUP_SUPPORTED;
+    }
 #endif
     path->length = length;
     path->object = o;
     path->fd = -1;
-    if (bytes == o) {
-        Py_DECREF(bytes);
-        ret = 1;
-    }
-    else {
-        path->cleanup = bytes;
-        ret = Py_CLEANUP_SUPPORTED;
-    }
- exit:
-    Py_XDECREF(to_cleanup);
+    goto success_exit;
+ error_exit:
+    Py_XDECREF(o);
+    Py_XDECREF(bytes);
+#ifdef MS_WINDOWS
+    Py_XDECREF(wo);
+#endif
+ success_exit:
     return ret;
 }