diff --git a/tests/regressiontests/utils/dateformat.py b/tests/regressiontests/utils/dateformat.py
index 6afbcd61ec..2ff3441486 100644
--- a/tests/regressiontests/utils/dateformat.py
+++ b/tests/regressiontests/utils/dateformat.py
@@ -6,11 +6,14 @@ from django.utils.tzinfo import FixedOffset, LocalTimezone
 
 class DateFormatTests(TestCase):
     def setUp(self):
-        self.old_TZ = os.environ['TZ']
+        self.old_TZ = os.environ.get('TZ')
         os.environ['TZ'] = 'Europe/Copenhagen'
 
     def tearDown(self):
-        os.environ['TZ'] = self.old_TZ
+        if self.old_TZ is None:
+            del os.environ['TZ']
+        else:
+            os.environ['TZ'] = self.old_TZ
 
     def test_date(self):
         d = date(2009, 5, 16)