diff --git a/python/subunit/__init__.py b/python/subunit/__init__.py
index 17a970a..63c7d66 100644
--- a/python/subunit/__init__.py
+++ b/python/subunit/__init__.py
@@ -799,7 +799,7 @@ class TestProtocolClient(testresult.TestResult):
 
         ":param datetime: A datetime.datetime object.
         """
-        time = a_datetime.astimezone(iso8601.Utc())
+        time = a_datetime.astimezone(iso8601.UTC)
         self._stream.write(_b("time: %04d-%02d-%02d %02d:%02d:%02d.%06dZ\n" % (
             time.year, time.month, time.day, time.hour, time.minute,
             time.second, time.microsecond)))
diff --git a/python/subunit/test_results.py b/python/subunit/test_results.py
index 53c3dad..3cda44a 100644
--- a/python/subunit/test_results.py
+++ b/python/subunit/test_results.py
@@ -196,7 +196,7 @@ class AutoTimingTestResultDecorator(HookedTestResultDecorator):
         time = self._time
         if time is not None:
             return
-        time = datetime.datetime.utcnow().replace(tzinfo=iso8601.Utc())
+        time = datetime.datetime.utcnow().replace(tzinfo=iso8601.UTC)
         self.decorated.time(time)
 
     def progress(self, offset, whence):
diff --git a/python/subunit/tests/test_test_protocol.py b/python/subunit/tests/test_test_protocol.py
index 7427b12..7692489 100644
--- a/python/subunit/tests/test_test_protocol.py
+++ b/python/subunit/tests/test_test_protocol.py
@@ -993,7 +993,7 @@ class TestTestProtocolServerStreamTime(unittest.TestCase):
         self.assertEqual(_b(""), self.stream.getvalue())
         self.assertEqual([
             ('time', datetime.datetime(2001, 12, 12, 12, 59, 59, 0,
-            iso8601.Utc()))
+            iso8601.UTC))
             ], self.result._events)
 
 
@@ -1368,7 +1368,7 @@ class TestTestProtocolClient(TestCase):
     def test_time(self):
         # Calling time() outputs a time signal immediately.
         self.protocol.time(
-            datetime.datetime(2009,10,11,12,13,14,15, iso8601.Utc()))
+            datetime.datetime(2009,10,11,12,13,14,15, iso8601.UTC))
         self.assertEqual(
             _b("time: 2009-10-11 12:13:14.000015Z\n"),
             self.io.getvalue())
diff --git a/python/subunit/tests/test_test_protocol2.py b/python/subunit/tests/test_test_protocol2.py
index bbf510e..f970ed6 100644
--- a/python/subunit/tests/test_test_protocol2.py
+++ b/python/subunit/tests/test_test_protocol2.py
@@ -218,7 +218,7 @@ class TestStreamResultToBytes(TestCase):
 
     def test_timestamp(self):
         timestamp = datetime.datetime(2001, 12, 12, 12, 59, 59, 45,
-            iso8601.Utc())
+            iso8601.UTC)
         result, output = self._make_result()
         result.status(test_id="bar", test_status='success', timestamp=timestamp)
         self.assertEqual(CONSTANT_TIMESTAMP, output.getvalue())
@@ -382,7 +382,7 @@ class TestByteStreamToStreamResult(TestCase):
 
     def test_timestamp(self):
         timestamp = datetime.datetime(2001, 12, 12, 12, 59, 59, 45,
-            iso8601.Utc())
+            iso8601.UTC)
         self.check_event(CONSTANT_TIMESTAMP,
             'success', test_id='bar', timestamp=timestamp)
 
diff --git a/python/subunit/tests/test_test_results.py b/python/subunit/tests/test_test_results.py
index 44f95b3..f1a83fd 100644
--- a/python/subunit/tests/test_test_results.py
+++ b/python/subunit/tests/test_test_results.py
@@ -178,7 +178,7 @@ class TestAutoTimingTestResultDecorator(unittest.TestCase):
     def test_calling_time_inhibits_automatic_time(self):
         # Calling time() outputs a time signal immediately and prevents
         # automatically adding one when other methods are called.
-        time = datetime.datetime(2009,10,11,12,13,14,15, iso8601.Utc())
+        time = datetime.datetime(2009,10,11,12,13,14,15, iso8601.UTC)
         self.result.time(time)
         self.result.startTest(self)
         self.result.stopTest(self)
@@ -186,7 +186,7 @@ class TestAutoTimingTestResultDecorator(unittest.TestCase):
         self.assertEqual(time, self.decorated._calls[0])
 
     def test_calling_time_None_enables_automatic_time(self):
-        time = datetime.datetime(2009,10,11,12,13,14,15, iso8601.Utc())
+        time = datetime.datetime(2009,10,11,12,13,14,15, iso8601.UTC)
         self.result.time(time)
         self.assertEqual(1, len(self.decorated._calls))
         self.assertEqual(time, self.decorated._calls[0])
diff --git a/python/subunit/v2.py b/python/subunit/v2.py
index e8a31d6..c299cab 100644
--- a/python/subunit/v2.py
+++ b/python/subunit/v2.py
@@ -49,7 +49,7 @@ FLAG_TAGS = 0x0080
 FLAG_MIME_TYPE = 0x0020
 FLAG_EOF = 0x0010
 FLAG_FILE_CONTENT = 0x0040
-EPOCH = datetime.datetime.utcfromtimestamp(0).replace(tzinfo=iso8601.Utc())
+EPOCH = datetime.datetime.utcfromtimestamp(0).replace(tzinfo=iso8601.UTC)
 NUL_ELEMENT = b'\0'[0]
 # Contains True for types for which 'nul in thing' falsely returns false.
 _nul_test_broken = {}