diff --git a/Lib/test/test_httpservers.py b/Lib/test/test_httpservers.py
--- a/Lib/test/test_httpservers.py
+++ b/Lib/test/test_httpservers.py
@@ -69,6 +69,7 @@ class TestServerThread(threading.Thread)
 
 class BaseTestCase(unittest.TestCase):
     def setUp(self):
+        os.environ = support.EnvironmentVarGuard()
         self.server_started = threading.Event()
         self.thread = TestServerThread(self, self.request_handler)
         self.thread.start()
@@ -76,6 +77,7 @@ class BaseTestCase(unittest.TestCase):
 
     def tearDown(self):
         self.thread.stop()
+        os.environ.__exit__()
 
     def request(self, uri, method='GET', body=None, headers={}):
         self.connection = http.client.HTTPConnection('localhost', self.PORT)