diff --git a/oslo_utils/tests/test_timeutils.py b/oslo_utils/tests/test_timeutils.py
index b1b1f8a7..77b1aa13 100644
--- a/oslo_utils/tests/test_timeutils.py
+++ b/oslo_utils/tests/test_timeutils.py
@@ -87,20 +87,18 @@ class TimeUtilsTest(test_base.BaseTestCase):
         t = timeutils.parse_strtime(s)
         self.assertEqual(orig_t, t)
 
-    def _test_is_older_than(self, fn):
-        strptime = datetime.datetime.strptime
-        with mock.patch('datetime.datetime') as datetime_mock:
-            datetime_mock.utcnow.return_value = self.skynet_self_aware_time
-            datetime_mock.strptime = strptime
-            expect_true = timeutils.is_older_than(fn(self.one_minute_before),
-                                                  59)
-            self.assertTrue(expect_true)
-            expect_false = timeutils.is_older_than(fn(self.one_minute_before),
-                                                   60)
-            self.assertFalse(expect_false)
-            expect_false = timeutils.is_older_than(fn(self.one_minute_before),
-                                                   61)
-            self.assertFalse(expect_false)
+    @mock.patch('datetime.datetime', wraps=datetime.datetime)
+    def _test_is_older_than(self, fn, datetime_mock):
+        datetime_mock.utcnow.return_value = self.skynet_self_aware_time
+        expect_true = timeutils.is_older_than(fn(self.one_minute_before),
+                                              59)
+        self.assertTrue(expect_true)
+        expect_false = timeutils.is_older_than(fn(self.one_minute_before),
+                                               60)
+        self.assertFalse(expect_false)
+        expect_false = timeutils.is_older_than(fn(self.one_minute_before),
+                                               61)
+        self.assertFalse(expect_false)
 
     def test_is_older_than_datetime(self):
         self._test_is_older_than(lambda x: x)
@@ -118,20 +116,18 @@ class TimeUtilsTest(test_base.BaseTestCase):
             tzinfo=iso8601.iso8601.FixedOffset(1, 0, 'foo')).replace(
                 hour=7))
 
-    def _test_is_newer_than(self, fn):
-        strptime = datetime.datetime.strptime
-        with mock.patch('datetime.datetime') as datetime_mock:
-            datetime_mock.utcnow.return_value = self.skynet_self_aware_time
-            datetime_mock.strptime = strptime
-            expect_true = timeutils.is_newer_than(fn(self.one_minute_after),
-                                                  59)
-            self.assertTrue(expect_true)
-            expect_false = timeutils.is_newer_than(fn(self.one_minute_after),
-                                                   60)
-            self.assertFalse(expect_false)
-            expect_false = timeutils.is_newer_than(fn(self.one_minute_after),
-                                                   61)
-            self.assertFalse(expect_false)
+    @mock.patch('datetime.datetime', wraps=datetime.datetime)
+    def _test_is_newer_than(self, fn, datetime_mock):
+        datetime_mock.utcnow.return_value = self.skynet_self_aware_time
+        expect_true = timeutils.is_newer_than(fn(self.one_minute_after),
+                                              59)
+        self.assertTrue(expect_true)
+        expect_false = timeutils.is_newer_than(fn(self.one_minute_after),
+                                               60)
+        self.assertFalse(expect_false)
+        expect_false = timeutils.is_newer_than(fn(self.one_minute_after),
+                                               61)
+        self.assertFalse(expect_false)
 
     def test_is_newer_than_datetime(self):
         self._test_is_newer_than(lambda x: x)
diff --git a/oslo_utils/timeutils.py b/oslo_utils/timeutils.py
index d467972b..e8eb9905 100644
--- a/oslo_utils/timeutils.py
+++ b/oslo_utils/timeutils.py
@@ -55,7 +55,8 @@ def isotime(at=None, subsecond=False):
                      if not subsecond
                      else _ISO8601_TIME_FORMAT_SUBSECOND)
     tz = at.tzinfo.tzname(None) if at.tzinfo else 'UTC'
-    st += ('Z' if tz == 'UTC' else tz)
+    # Need to handle either iso8601 or python UTC format
+    st += ('Z' if tz in ('UTC', 'UTC+00:00') else tz)
     return st
 
 
@@ -256,7 +257,9 @@ def marshall_now(now=None):
              minute=now.minute, second=now.second,
              microsecond=now.microsecond)
     if now.tzinfo:
-        d['tzname'] = now.tzinfo.tzname(None)
+        # Need to handle either iso8601 or python UTC format
+        tzname = now.tzinfo.tzname(None)
+        d['tzname'] = 'UTC' if tzname == 'UTC+00:00' else tzname
     return d
 
 
@@ -283,6 +286,8 @@ def unmarshall_time(tyme):
                            microsecond=tyme['microsecond'])
     tzname = tyme.get('tzname')
     if tzname:
+        # Need to handle either iso8601 or python UTC format
+        tzname = 'UTC' if tzname == 'UTC+00:00' else tzname
         tzinfo = pytz.timezone(tzname)
         dt = tzinfo.localize(dt)
     return dt