diff --git a/django/utils/timezone.py b/django/utils/timezone.py
index 9e78134d2a..16e65fc62d 100644
--- a/django/utils/timezone.py
+++ b/django/utils/timezone.py
@@ -102,8 +102,10 @@ def get_default_timezone():
     """
     global _localtime
     if _localtime is None:
-        tz = settings.TIME_ZONE
-        _localtime = pytz.timezone(tz) if pytz else LocalTimezone()
+        if isinstance(settings.TIME_ZONE, basestring) and pytz is not None:
+            _localtime = pytz.timezone(settings.TIME_ZONE)
+        else:
+            _localtime = LocalTimezone()
     return _localtime
 
 # This function exists for consistency with get_current_timezone_name
diff --git a/tests/modeltests/timezones/tests.py b/tests/modeltests/timezones/tests.py
index a2f4ad2029..53b14045ab 100644
--- a/tests/modeltests/timezones/tests.py
+++ b/tests/modeltests/timezones/tests.py
@@ -774,6 +774,17 @@ class TemplateTests(BaseDateTimeTests):
         with timezone.override(ICT):
             self.assertEqual(tpl.render(ctx), "2011-09-01 at 20:20:20")
 
+    def test_localtime_with_time_zone_setting_set_to_none(self):
+        # Regression for #17274
+        tpl = Template("{% load tz %}{{ dt }}")
+        ctx = Context({'dt': datetime.datetime(2011, 9, 1, 12, 20, 30, tzinfo=EAT)})
+
+        timezone._localtime = None
+        with self.settings(TIME_ZONE=None):
+            # the actual value depends on the system time zone of the host
+            self.assertTrue(tpl.render(ctx).startswith("2011"))
+        timezone._localtime = None
+
 TemplateTests = override_settings(DATETIME_FORMAT='c', USE_L10N=False, USE_TZ=True)(TemplateTests)
 
 #@override_settings(DATETIME_FORMAT='c', USE_L10N=False, USE_TZ=False)