Index: Lib/test/test_sys.py
===================================================================
--- Lib/test/test_sys.py	(revision 81886)
+++ Lib/test/test_sys.py	(working copy)
@@ -868,6 +868,15 @@
         if sys.platform == 'darwin':
             self.assertEqual(fs_encoding, 'utf-8')
 
+            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()
         try: