diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
index 7f96a33e..8c2fab8a 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
@@ -1024,9 +1024,8 @@ class AndroidCalendarDataSource @Inject constructor(
             updateEventRow(eventId, values.toContentValues(), "update event id=$eventId")
         }
         // Untouched reminder sets are left alone so unrelated edits can't
-        // disturb provider rows the form never knew about. The diff is on the
-        // form's semantic minutes; reconcile works in encoded provider minutes.
-        if (updated.reminders.toSet() != original.reminders.toSet()) {
+        // disturb provider rows the form never knew about.
+        if (remindersNeedRewrite(original, updated)) {
             reconcileReminders(eventId, encodedReminders(updated, allDayReminderTimeMinutes))
         }
         // Same untouched-set guard for guests: only reconcile when the form's
@@ -1785,3 +1784,11 @@ class AndroidCalendarDataSource @Inject constructor(
         const val MAX_SEARCH_TOKENS = 8
     }
 }
+
+/**
+ * Whether an update must rewrite the reminder rows. The diff is on the form's
+ * semantic minutes, but the provider stores encoded minutes, so switching all-day
+ * on or off re-encodes an otherwise unchanged set.
+ */
+internal fun remindersNeedRewrite(original: EventForm, updated: EventForm): Boolean =
+    updated.reminders.toSet() != original.reminders.toSet() || updated.isAllDay != original.isAllDay
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt b/app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt
index 041642a2..2accd39d 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt
@@ -538,9 +538,10 @@ class EventEditViewModel @Inject constructor(
             if (opened != session) return@launch
             val current = _form.value ?: return@launch
             if (_editTarget.value != null) return@launch
-            if (default.isEmpty() || default == current.firingReminders()) return@launch
+            val firing = current.firingReminders()
+            if (default.isEmpty() || default == firing) return@launch
             _importReminderPrompt.value = ImportReminderPrompt(
-                currentReminderCount = current.firingReminders().size,
+                currentReminderCount = firing.size,
                 defaultReminders = default,
             )
         }
@@ -967,7 +968,7 @@ class EventEditViewModel @Inject constructor(
 /**
  * Reminders as they fire: an all-day event fires on whole days, so a sub-day lead
  * time kept from the timed form reads as its day. The form keeps the raw values,
- * so switching all-day off again restores them.
+ * so switching all-day off again restores any the user did not remove.
  */
 internal fun EventForm.firingReminders(): List<Int> =
     if (isAllDay) wholeDayLeadTimes(reminders) else reminders
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapperTest.kt b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapperTest.kt
index a783bafe..9cd03414 100644
--- a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapperTest.kt
+++ b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapperTest.kt
@@ -33,6 +33,14 @@ class EventWriteMapperTest {
         timezone = timezone,
     )
 
+    @Test
+    fun `reminders are rewritten when they change or the all-day flag flips`() {
+        val timed = form().copy(reminders = listOf(10))
+        assertThat(remindersNeedRewrite(timed, timed.copy(title = "Renamed"))).isFalse()
+        assertThat(remindersNeedRewrite(timed, timed.copy(reminders = listOf(10, 30)))).isTrue()
+        assertThat(remindersNeedRewrite(timed, timed.copy(isAllDay = true))).isTrue()
+    }
+
     @Test
     fun `timed event resolves wall clock in the given zone`() {
         val times = form().toWriteTimes(berlin)