diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -270,8 +270,12 @@
         self.assertEqual(out1, out2)
 
     def test_displayhook_unencodable(self):
+        # This test involves an environment variable, this means that
+        # it can't, by definition not use the '-E' or '-I' executable
+        # parameters. And hence, can't use script_helper.spawn_python
         for encoding in ('ascii', 'latin-1', 'utf-8'):
-            env = os.environ.copy()
+            env = {key:value for (key,value) in os.environ.copy().items()
+                   if not key.startswith('PYTHON')}
             env['PYTHONIOENCODING'] = encoding
             p = subprocess.Popen(
                 [sys.executable, '-i'],