diff -r 7f30206d402f Lib/test/test_file.py
--- a/Lib/test/test_file.py	Tue Jan 06 12:39:45 2015 +0100
+++ b/Lib/test/test_file.py	Tue Jan 06 12:42:04 2015 +0100
@@ -154,6 +154,22 @@ class OtherFileTests(unittest.TestCase):
                 f.close()
                 self.fail('%r is an invalid file mode' % mode)
 
+    def testStdinSeek(self):
+        if sys.platform == 'osf1V5':
+            # This causes the interpreter to exit on OSF1 v5.1.
+            self.skipTest('Skipping sys.stdin.seek(-1), it may crash '
+                          'the interpreter. Test manually.')
+
+        if not sys.stdin.isatty():
+            # Issue #23168: if stdin is redirected to a file, stdin becomes
+            # seekable
+            self.skipTest('stdin must be a TTY in this test')
+
+        self.assertRaises(IOError, sys.stdin.seek, -1)
+
+    def testStdinTruncate(self):
+        self.assertRaises(IOError, sys.stdin.truncate)
+
     def testBadModeArgument(self):
         # verify that we get a sensible error message for bad mode argument
         bad_mode = "qwerty"