diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/EventReminderReceiver.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/EventReminderReceiver.kt
index 62078c9..dc6871f 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/EventReminderReceiver.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/EventReminderReceiver.kt
@@ -17,6 +17,17 @@ import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
+/**
+ * The due alerts that should actually surface as notifications: everything
+ * except alerts whose calendar the user has disabled in-app (mirroring the
+ * event filtering in CalendarRepositoryImpl). The caller still marks the full
+ * due set fired, so suppressed alerts are not re-broadcast by the provider.
+ */
+internal fun postableAlerts(
+    due: List<ReminderAlert>,
+    disabledCalendarIds: Set<Long>,
+): List<ReminderAlert> = due.filterNot { it.calendarId in disabledCalendarIds }
+
 /**
  * Becomes the app that turns the calendar provider's reminder alarms into
  * visible notifications (the Etar model — the provider broadcasts
@@ -48,13 +59,11 @@ class EventReminderReceiver : BroadcastReceiver() {
                 if (settingsPrefs.remindersEnabled.first()) {
                     val now = System.currentTimeMillis()
                     val due = alertStore.dueAlerts(now)
-                    // Suppress reminders for calendars the user disabled in-app
-                    // (mirrors the event filtering in CalendarRepositoryImpl), but
-                    // still mark every due alert fired so the provider stops
-                    // re-broadcasting the suppressed ones.
                     val disabled = calendarPrefs.disabledCalendarIds.first()
-                    due.filterNot { it.calendarId in disabled }
-                        .forEach { notifier.post(it) }
+                    // Suppress reminders for disabled calendars, but still mark
+                    // every due alert fired so the provider stops re-broadcasting
+                    // the suppressed ones.
+                    postableAlerts(due, disabled).forEach { notifier.post(it) }
                     alertStore.markFired(due.map { it.alertId }, now)
                 }
             } finally {
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/data/reminders/PostableAlertsTest.kt b/app/src/test/java/de/jeanlucmakiola/calendula/data/reminders/PostableAlertsTest.kt
new file mode 100644
index 0000000..222281e
--- /dev/null
+++ b/app/src/test/java/de/jeanlucmakiola/calendula/data/reminders/PostableAlertsTest.kt
@@ -0,0 +1,55 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class PostableAlertsTest {
+
+    private fun alert(alertId: Long, calendarId: Long) = ReminderAlert(
+        alertId = alertId,
+        eventId = alertId * 10,
+        calendarId = calendarId,
+        beginMillis = 0L,
+        endMillis = 0L,
+        title = "Event $alertId",
+        location = null,
+        isAllDay = false,
+    )
+
+    @Test
+    fun `keeps alerts when no calendar is disabled`() {
+        val due = listOf(alert(1, calendarId = 100), alert(2, calendarId = 200))
+
+        val postable = postableAlerts(due, disabledCalendarIds = emptySet())
+
+        assertThat(postable).isEqualTo(due)
+    }
+
+    @Test
+    fun `drops alerts for a disabled calendar`() {
+        val keep = alert(1, calendarId = 100)
+        val drop = alert(2, calendarId = 200)
+
+        val postable = postableAlerts(listOf(keep, drop), disabledCalendarIds = setOf(200))
+
+        assertThat(postable).containsExactly(keep)
+    }
+
+    @Test
+    fun `drops every alert when all their calendars are disabled`() {
+        val due = listOf(alert(1, calendarId = 100), alert(2, calendarId = 100))
+
+        val postable = postableAlerts(due, disabledCalendarIds = setOf(100))
+
+        assertThat(postable).isEmpty()
+    }
+
+    @Test
+    fun `keeps multiple alerts from the same enabled calendar`() {
+        val due = listOf(alert(1, calendarId = 100), alert(2, calendarId = 100))
+
+        val postable = postableAlerts(due, disabledCalendarIds = setOf(999))
+
+        assertThat(postable).isEqualTo(due)
+    }
+}