diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index 13aa7b3..2a9590a 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -120,8 +120,8 @@
         # Records changes to env vars
         self.env = support.EnvironmentVarGuard()
         # Delete all proxy related env vars
-        for k in os.environ.keys():
-            if k == 'NO_PROXY':
+        for k in list(os.environ):
+            if 'proxy' in k.lower():
                 self.env.unset(k)
 
     def tearDown(self):