#15222: Fix a test failure on Windows
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 84c6cdd..0696fef 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -145,7 +145,7 @@
         key1 = self._box.add(self._template % 1)
         msg = self._box.get(key1)
         self.assertEqual(msg['from'], 'foo')
-        self.assertEqual(msg.fp.read(), '1\n')
+        self.assertEqual(msg.fp.read(), '1' + os.linesep)
 
     def test_getitem(self):
         # Retrieve message using __getitem__()