diff --git a/synctools/src/main/kotlin/at/bitfire/synctools/icalendar/ICalendarGenerator.kt b/synctools/src/main/kotlin/at/bitfire/synctools/icalendar/ICalendarGenerator.kt
index 4ab142ae33..49d43c844c 100644
--- a/synctools/src/main/kotlin/at/bitfire/synctools/icalendar/ICalendarGenerator.kt
+++ b/synctools/src/main/kotlin/at/bitfire/synctools/icalendar/ICalendarGenerator.kt
@@ -5,6 +5,7 @@
 package at.bitfire.synctools.icalendar
 
 import androidx.annotation.VisibleForTesting
+import at.bitfire.synctools.util.AndroidTimeUtils.toInstant
 import at.bitfire.synctools.util.Utils.trimToNull
 import net.fortuna.ical4j.data.CalendarOutputter
 import net.fortuna.ical4j.model.Calendar
@@ -13,7 +14,6 @@ import net.fortuna.ical4j.model.ComponentList
 import net.fortuna.ical4j.model.Parameter
 import net.fortuna.ical4j.model.PropertyContainer
 import net.fortuna.ical4j.model.PropertyList
-import net.fortuna.ical4j.model.TemporalAdapter
 import net.fortuna.ical4j.model.TimeZoneRegistryFactory
 import net.fortuna.ical4j.model.component.VEvent
 import net.fortuna.ical4j.model.component.VTimeZone
@@ -66,7 +66,10 @@ class ICalendarGenerator {
             ical += exception
 
             exception.dtStart<Temporal>()?.date?.let { start ->
-                if (earliestStart == null || TemporalAdapter.isBefore(start, earliestStart))
+                // Convert both Temporals to Instants for comparison because they may be in different time zones. If conversion fails, UnsupportedTemporalTypeException is thrown.
+                val startInstant = start.toInstant()
+                val earliestInstant = start.toInstant()
+                if (startInstant < earliestInstant)
                     earliestStart = start
             }
             usedTimezoneIds += timeZonesOf(exception)
diff --git a/synctools/src/test/kotlin/at/bitfire/synctools/icalendar/ICalendarGeneratorTest.kt b/synctools/src/test/kotlin/at/bitfire/synctools/icalendar/ICalendarGeneratorTest.kt
index 96d9ba294b..7673098a53 100644
--- a/synctools/src/test/kotlin/at/bitfire/synctools/icalendar/ICalendarGeneratorTest.kt
+++ b/synctools/src/test/kotlin/at/bitfire/synctools/icalendar/ICalendarGeneratorTest.kt
@@ -246,4 +246,27 @@ class ICalendarGeneratorTest {
         assertTrue(result.isEmpty())
     }
 
+    @Test
+    fun `Write event with UTC Instant exception DTSTART does not throw`() {
+        val iCal = StringWriter()
+        writer.write(AssociatedEvents(
+            main = VEvent(propertyListOf(
+                Uid("UTCTEST"),
+                DtStart(ZonedDateTime.of(LocalDateTime.parse("2025-08-22T05:30:00"), tzBerlin)),
+                DtStamp("20250822T000000Z"),
+                RRule<Temporal>("FREQ=DAILY;COUNT=3")
+            )),
+            exceptions = listOf(
+                VEvent(propertyListOf(
+                    Uid("UTCTEST"),
+                    RecurrenceId(Instant.parse("2025-08-22T03:30:00Z")),
+                    DtStart(Instant.parse("2025-08-22T03:30:00Z")),
+                    DtStamp("20250822T000000Z")
+                ))
+            ),
+            prodId = userAgent
+        ), iCal)
+        assertTrue(iCal.toString().contains("BEGIN:VCALENDAR"))
+    }
+
 }
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