diff --git a/Lib/distutils/tests/test_build_ext.py b/Lib/distutils/tests/test_build_ext.py
index a4494db..a6d2d2e 100644
--- a/Lib/distutils/tests/test_build_ext.py
+++ b/Lib/distutils/tests/test_build_ext.py
@@ -20,6 +20,7 @@
 
 class BuildExtTestCase(support.TempdirManager,
                        support.LoggingSilencer,
+                       support.EnvironGuard,
                        unittest.TestCase):
     def setUp(self):
         super(BuildExtTestCase, self).setUp()