diff --git a/Misc/NEWS b/Misc/NEWS
index 00ae970d8bf..35add804d0f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,12 @@ What's New in Python 3.4.0 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #16416: OS data are now always encoded/decoded to/from
+  UTF-8/surrogateescape, instead of the locale encoding (which may be ASCII if
+  no locale environment variable is set), to avoid inconsistencies with
+  os.fsencode() and os.fsdecode() functions which are already using
+  UTF-8/surrogateescape.
+
 - Issue #16453: Fix equality testing of dead weakref objects.
 
 - Issue #9535: Fix pending signals that have been received but not yet
diff --git a/Modules/python.c b/Modules/python.c
index c70bf378279..2c08b968568 100644
--- a/Modules/python.c
+++ b/Modules/python.c
@@ -15,10 +15,6 @@ wmain(int argc, wchar_t **argv)
 }
 #else
 
-#ifdef __APPLE__
-extern wchar_t* _Py_DecodeUTF8_surrogateescape(const char *s, Py_ssize_t size);
-#endif
-
 int
 main(int argc, char **argv)
 {
@@ -45,11 +41,7 @@ main(int argc, char **argv)
     oldloc = strdup(setlocale(LC_ALL, NULL));
     setlocale(LC_ALL, "");
     for (i = 0; i < argc; i++) {
-#ifdef __APPLE__
-        argv_copy[i] = _Py_DecodeUTF8_surrogateescape(argv[i], strlen(argv[i]));
-#else
         argv_copy[i] = _Py_char2wchar(argv[i], NULL);
-#endif
         if (!argv_copy[i]) {
             free(oldloc);
             fprintf(stderr, "Fatal Python error: "
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 2e25aae0755..42a532d9fa9 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -8,6 +8,10 @@
 #include <langinfo.h>
 #endif
 
+#ifdef __APPLE__
+extern wchar_t* _Py_DecodeUTF8_surrogateescape(const char *s, Py_ssize_t size);
+#endif
+
 PyObject *
 _Py_device_encoding(int fd)
 {
@@ -60,6 +64,15 @@ _Py_device_encoding(int fd)
 wchar_t*
 _Py_char2wchar(const char* arg, size_t *size)
 {
+#ifdef __APPLE__
+    wchar_t *wstr;
+    wstr = _Py_DecodeUTF8_surrogateescape(arg, strlen(arg));
+    if (wstr == NULL)
+        return NULL;
+    if (size != NULL)
+        *size = wcslen(wstr);
+    return wstr;
+#else
     wchar_t *res;
 #ifdef HAVE_BROKEN_MBSTOWCS
     /* Some platforms have a broken implementation of
@@ -145,7 +158,7 @@ _Py_char2wchar(const char* arg, size_t *size)
         argsize -= converted;
         out++;
     }
-#else
+#else   /* HAVE_MBRTOWC */
     /* Cannot use C locale for escaping; manually escape as if charset
        is ASCII (i.e. escape all bytes > 128. This will still roundtrip
        correctly in the locale's charset, which must be an ASCII superset. */
@@ -160,7 +173,7 @@ _Py_char2wchar(const char* arg, size_t *size)
         else
             *out++ = 0xdc00 + *in++;
     *out = 0;
-#endif
+#endif   /* HAVE_MBRTOWC */
     if (size != NULL)
         *size = out - res;
     return res;
@@ -168,6 +181,7 @@ oom:
     if (size != NULL)
         *size = (size_t)-1;
     return NULL;
+#endif   /* __APPLE__ */
 }
 
 /* Encode a (wide) character string to the locale encoding with the
@@ -184,6 +198,34 @@ oom:
 char*
 _Py_wchar2char(const wchar_t *text, size_t *error_pos)
 {
+#ifdef __APPLE__
+    Py_ssize_t len;
+    PyObject *unicode, *bytes = NULL;
+    char *cpath;
+
+    unicode = PyUnicode_FromWideChar(text, wcslen(text));
+    if (unicode == NULL) {
+        Py_DECREF(unicode);
+        return NULL;
+    }
+
+    bytes = _PyUnicode_AsUTF8String(unicode, "surrogateescape");
+    Py_DECREF(unicode);
+    if (bytes == NULL) {
+        PyErr_Clear();
+        return NULL;
+    }
+
+    len = PyBytes_GET_SIZE(bytes);
+    cpath = PyMem_Malloc(len+1);
+    if (cpath == NULL) {
+        Py_DECREF(bytes);
+        return NULL;
+    }
+    memcpy(cpath, PyBytes_AsString(bytes), len + 1);
+    Py_DECREF(bytes);
+    return cpath;
+#else   /* __APPLE__ */
     const size_t len = wcslen(text);
     char *result = NULL, *bytes = NULL;
     size_t i, size, converted;
@@ -243,6 +285,7 @@ _Py_wchar2char(const wchar_t *text, size_t *error_pos)
         bytes = result;
     }
     return result;
+#endif   /* __APPLE__ */
 }
 
 /* In principle, this should use HAVE__WSTAT, and _wstat