diff -r bfe8ef6e370e -r 57b0c7221dba tests/test-encoding-func.py
--- a/tests/test-encoding-func.py	Sun Mar 25 16:47:33 2018 +0900
+++ b/tests/test-encoding-func.py	Sun Apr 22 11:38:53 2018 +0900
@@ -35,11 +35,32 @@
         self.assertTrue(s is encoding.fromlocal(s))
 
 class Utf8bEncodingTest(unittest.TestCase):
+    def setUp(self):
+        self.origencoding = encoding.encoding
+
+    def tearDown(self):
+        encoding.encoding = self.origencoding
+
     def testasciifastpath(self):
         s = b'\0' * 100
         self.assertTrue(s is encoding.toutf8b(s))
         self.assertTrue(s is encoding.fromutf8b(s))
 
+    def testlossylatin(self):
+        encoding.encoding = b'ascii'
+        s = u'\xc0'.encode('utf-8')
+        l = encoding.tolocal(s)
+        self.assertEqual(l, b'?')  # lossy
+        self.assertEqual(s, encoding.toutf8b(l))  # utf8 sequence preserved
+
+    def testlossy0xed(self):
+        encoding.encoding = b'euc-kr'  # U+Dxxx Hangul
+        s = u'\ud1bc\xc0'.encode('utf-8')
+        l = encoding.tolocal(s)
+        self.assertIn(b'\xed', l)
+        self.assertTrue(l.endswith(b'?'))  # lossy
+        self.assertEqual(s, encoding.toutf8b(l))  # utf8 sequence preserved
+
 if __name__ == '__main__':
     import silenttestrunner
     silenttestrunner.main(__name__)