Index: Lib/test/test_urllib.py
===================================================================
--- Lib/test/test_urllib.py	(revision 68226)
+++ Lib/test/test_urllib.py	(working copy)
@@ -131,9 +131,13 @@
 
     def test_getproxies_environment_keep_no_proxies(self):
         os.environ['NO_PROXY'] = 'localhost'
-        proxies = urllib.request.getproxies_environment()
-        # getproxies_environment use lowered case truncated (no '_proxy') keys
-        self.assertEquals('localhost', proxies['no'])
+        try:
+            proxies = urllib.request.getproxies_environment()
+            # getproxies_environment use lowered case truncated
+            # (no '_proxy') keys
+            self.assertEquals('localhost', proxies['no'])
+        finally:
+            del os.environ['NO_PROXY']
 
 
 class urlopen_HttpTests(unittest.TestCase):