diff --git a/setup.py b/setup.py
index 01a8a84..93b3778 100644
--- a/setup.py
+++ b/setup.py
@@ -21,6 +21,9 @@ tests_require = []
 install_requires = [
     'python-dateutil',
     'pytz',
+    # install requirements depending on python version
+    # see https://www.python.org/dev/peps/pep-0508/#environment-markers
+    'backports.zoneinfo; python_version == "3.7" or python_version == "3.8"',
 ]
 
 
diff --git a/src/icalendar/tests/test_fixed_issues.py b/src/icalendar/tests/test_fixed_issues.py
index 423e71b..15bc377 100644
--- a/src/icalendar/tests/test_fixed_issues.py
+++ b/src/icalendar/tests/test_fixed_issues.py
@@ -5,7 +5,13 @@ import datetime
 import icalendar
 import os
 import pytz
+import pytest
+from dateutil import tz
 
+try:
+    import zoneinfo
+except ModuleNotFoundError:
+    from backports import zoneinfo
 
 class TestIssues(unittest.TestCase):
 
@@ -487,4 +493,15 @@ END:VCALENDAR"""
         self.assertEqual(uid2.split('@')[1], 'test.test')
         self.assertEqual(uid3.split('-')[1], '123@example.com')
         self.assertEqual(uid4.split('-')[1], '123@test.test')
-        
+
+@pytest.mark.parametrize("zone", [
+    pytz.utc,
+    zoneinfo.ZoneInfo('UTC'),
+    pytz.timezone('UTC'),
+    tz.UTC,
+    tz.gettz('UTC')])
+def test_issue_335_identify_UTC(zone):
+    myevent = icalendar.Event()
+    dt = datetime.datetime(2021, 11, 17, 15, 9, 15)
+    myevent.add('dtstart', dt.astimezone(zone))
+    assert 'DTSTART;VALUE=DATE-TIME:20211117T150915Z' in myevent.to_ical().decode('ASCII')
diff --git a/src/icalendar/tests/test_timezoned.py b/src/icalendar/tests/test_timezoned.py
index f93037b..7d5d499 100644
--- a/src/icalendar/tests/test_timezoned.py
+++ b/src/icalendar/tests/test_timezoned.py
@@ -8,17 +8,11 @@ import pytz
 try:
     import zoneinfo
 except:
-    try:
-        from backports import zoneinfo
-    except:
-        zoneinfo = None
+    from backports import zoneinfo
 
 class TestTimezoned(unittest.TestCase):
 
     def test_create_from_ical_zoneinfo(self):
-        if zoneinfo is None:
-            self.skipTest("zoneinfo library not found for this python version")
-            
         directory = os.path.dirname(__file__)
         with open(os.path.join(directory, 'timezoned.ics'), 'rb') as fp:
             data = fp.read()
@@ -172,9 +166,6 @@ class TestTimezoned(unittest.TestCase):
         self.assertTrue("CREATED;VALUE=DATE-TIME:20101010T081010Z" in test_out)
 
     def test_create_to_ical_zoneinfo(self):
-        if zoneinfo is None:
-            self.skipTest("zoneinfo library not found for this python version")
-
         cal = icalendar.Calendar()
 
         cal.add('prodid', "-//Plone.org//NONSGML plone.app.event//EN")