Index: Lib/test/test_sys.py
===================================================================
--- Lib/test/test_sys.py	(revision 81886)
+++ Lib/test/test_sys.py	(working copy)
@@ -865,8 +865,21 @@
 
     def test_getfilesystemencoding(self):
         fs_encoding = sys.getfilesystemencoding()
-        if sys.platform == 'darwin':
-            self.assertEqual(fs_encoding, 'utf-8')
+        if sys.platform != 'darwin':
+            # XXX: can we meaninfully check the result
+            # on other platforms?
+            return
+        # On Darwing FS encoding is always UTF-8
+        self.assertEqual(fs_encoding, 'utf-8')
+        # Even in C locale
+        env = os.environ.copy()
+        env['LANG'] = 'C'
+        output = subprocess.check_output(
+            [sys.executable, "-c",
+             "import sys; print(sys.getfilesystemencoding())"],
+            env=env)
+        fs_encoding = output.strip()
+        self.assertEqual(fs_encoding, b'utf-8')
 
     def test_setfilesystemencoding(self):
         old = sys.getfilesystemencoding()