diff --git a/agenda/trip.py b/agenda/trip.py
index 0aadcfb..b47e185 100644
--- a/agenda/trip.py
+++ b/agenda/trip.py
@@ -4,7 +4,7 @@ import decimal
 import hashlib
 import os
 import typing
-from datetime import date, datetime, timedelta, timezone, tzinfo as datetime_tzinfo
+from datetime import date, datetime, timedelta, timezone
 
 import flask
 import pycountry
@@ -548,43 +548,16 @@ def _append_ical_property(lines: list[str], name: str, value: str) -> None:
         lines.append(line)
 
 
-def _append_datetime_property(lines: list[str], name: str, dt_value: datetime) -> None:
-    """Append a datetime property preserving timezone."""
-    formatted, tzid = _format_ical_datetime(dt_value)
-    prop_name = f"{name};TZID={tzid}" if tzid else name
-    _append_ical_property(lines, prop_name, formatted)
-
-
-def _ensure_timezone(dt_value: datetime) -> datetime:
-    """Ensure datetimes are timezone-aware."""
-    if dt_value.tzinfo is None or dt_value.tzinfo.utcoffset(dt_value) is None:
+def _ensure_utc(dt_value: datetime) -> datetime:
+    """Ensure datetimes are timezone-aware in UTC."""
+    if dt_value.tzinfo is None:
         return dt_value.replace(tzinfo=timezone.utc)
-    return dt_value
+    return dt_value.astimezone(timezone.utc)
 
 
-def _tzid_from_tzinfo(tzinfo_obj: datetime_tzinfo, dt_value: datetime) -> str | None:
-    """Return TZID string for timezone-aware datetime."""
-    for attr in ("zone", "key"):
-        tzid = getattr(tzinfo_obj, attr, None)
-        if isinstance(tzid, str):
-            return tzid
-    tzname = tzinfo_obj.tzname(dt_value)
-    if isinstance(tzname, str) and tzname.upper() not in {"UTC", "GMT"}:
-        return tzname
-    return None
-
-
-def _format_ical_datetime(dt_value: datetime) -> tuple[str, str | None]:
-    """Format datetime objects, preserving timezone when available."""
-    dt_value = _ensure_timezone(dt_value)
-    tzinfo = dt_value.tzinfo
-    assert tzinfo
-    tzid = _tzid_from_tzinfo(tzinfo, dt_value)
-    if tzid:
-        local_dt = dt_value.astimezone(tzinfo).replace(tzinfo=None)
-        return local_dt.strftime("%Y%m%dT%H%M%S"), tzid
-    utc_dt = dt_value.astimezone(timezone.utc)
-    return utc_dt.strftime("%Y%m%dT%H%M%SZ"), None
+def _format_ical_datetime(dt_value: datetime) -> str:
+    """Format datetime objects using UTC and RFC5545 format."""
+    return _ensure_utc(dt_value).strftime("%Y%m%dT%H%M%SZ")
 
 
 def _format_ical_date(date_value: date) -> str:
@@ -598,7 +571,7 @@ def _event_datetimes(element: TripElement) -> tuple[datetime, datetime]:
     end_dt = as_datetime(element.end_time) if element.end_time else None
     if end_dt is None or end_dt <= start_dt:
         end_dt = start_dt + DEFAULT_EVENT_DURATION
-    return _ensure_timezone(start_dt), _ensure_timezone(end_dt)
+    return _ensure_utc(start_dt), _ensure_utc(end_dt)
 
 
 def _event_all_day_dates(element: TripElement) -> tuple[date, date]:
@@ -784,7 +757,7 @@ def build_trip_ical(trips: list[Trip]) -> bytes:
         for index, element in enumerate(trip.elements()):
             lines.append("BEGIN:VEVENT")
             _append_ical_property(lines, "UID", _trip_element_uid(trip, element, index))
-            _append_datetime_property(lines, "DTSTAMP", generated)
+            _append_ical_property(lines, "DTSTAMP", _format_ical_datetime(generated))
             if element.all_day:
                 start_date, end_date = _event_all_day_dates(element)
                 _append_ical_property(
@@ -795,8 +768,8 @@ def build_trip_ical(trips: list[Trip]) -> bytes:
                 )
             else:
                 start_dt, end_dt = _event_datetimes(element)
-                _append_datetime_property(lines, "DTSTART", start_dt)
-                _append_datetime_property(lines, "DTEND", end_dt)
+                _append_ical_property(lines, "DTSTART", _format_ical_datetime(start_dt))
+                _append_ical_property(lines, "DTEND", _format_ical_datetime(end_dt))
             summary = _escape_ical_text(_trip_element_summary(trip, element))
             _append_ical_property(lines, "SUMMARY", summary)