diff --git a/src/icalendar/tests/test_pytz_zoneinfo_integration.py b/src/icalendar/tests/test_pytz_zoneinfo_integration.py
new file mode 100644
index 0000000..c797c03
--- /dev/null
+++ b/src/icalendar/tests/test_pytz_zoneinfo_integration.py
@@ -0,0 +1,15 @@
+"""This tests the switch to different timezone implementations.
+
+These are mostly located in icalendar.timezone.
+"""
+import pytz
+from icalendar.timezone.zoneinfo import zoneinfo, ZONEINFO
+from icalendar.timezone.pytz import PYTZ
+import pytest
+
+
+@pytest.mark.parametrize("tz_name", pytz.all_timezones + list(zoneinfo.available_timezones()))
+@pytest.mark.parametrize("tzp_", [PYTZ(), ZONEINFO()])
+def test_timezone_names_are_known(tz_name, tzp_):
+    """Make sure that all timezones are understood."""
+    assert tzp_.knows_timezone_id(tz_name), f"{tzp_.__class__.__name__} should know {tz_name}"
diff --git a/src/icalendar/timezone/zoneinfo.py b/src/icalendar/timezone/zoneinfo.py
index b683e2b..ab3dde3 100644
--- a/src/icalendar/timezone/zoneinfo.py
+++ b/src/icalendar/timezone/zoneinfo.py
@@ -11,6 +11,7 @@ class ZONEINFO:
     """Provide icalendar with timezones from zoneinfo."""
 
     utc = zoneinfo.ZoneInfo("UTC")
+    _available_timezones = zoneinfo.available_timezones()
 
     def localize(self, dt: datetime, tz: zoneinfo.ZoneInfo) -> datetime:
         """Localize a datetime to a timezone."""
@@ -27,6 +28,9 @@ class ZONEINFO:
         except ValueError:
             pass
 
+    def knows_timezone_id(self, id: str) -> bool:
+        """Whether the timezone is already cached by the implementation."""
+        return id in self._available_timezones
 
 
 __all__ = ["ZONEINFO"]