diff --git a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/activities/TaskActivity.kt b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/activities/TaskActivity.kt
index 4765563bf..81ccfa0cc 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/activities/TaskActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/activities/TaskActivity.kt
@@ -376,6 +376,14 @@ class TaskActivity : SimpleActivity() {
             endTS = startTS
             title = newTitle
             description = task_description.value
+
+            // migrate completed task to the new completed tasks db
+            if (!wasRepeatable && mTask.isTaskCompleted()) {
+                mTask.flags = mTask.flags.removeBit(FLAG_TASK_COMPLETED)
+                ensureBackgroundThread {
+                    updateTaskCompletion(copy(startTS = mOriginalStartTS), true)
+                }
+            }
             flags = mTask.flags.addBitIf(task_all_day.isChecked, FLAG_ALL_DAY)
             lastUpdated = System.currentTimeMillis()
             eventType = mEventTypeId
diff --git a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/databases/EventsDatabase.kt b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/databases/EventsDatabase.kt
index 6199a71f7..65c9e1307 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/databases/EventsDatabase.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/databases/EventsDatabase.kt
@@ -123,7 +123,7 @@ abstract class EventsDatabase : RoomDatabase() {
             override fun migrate(database: SupportSQLiteDatabase) {
                 database.apply {
                     execSQL("CREATE TABLE IF NOT EXISTS `tasks` (`id` INTEGER PRIMARY KEY AUTOINCREMENT, `task_id` INTEGER NOT NULL, `start_ts` INTEGER NOT NULL, `flags` INTEGER NOT NULL)")
-                    execSQL("CREATE UNIQUE INDEX IF NOT EXISTS `index_tasks_id` ON `tasks` (`id`)")
+                    execSQL("CREATE UNIQUE INDEX IF NOT EXISTS `index_tasks_id_task_id` ON `tasks` (`id`, `task_id`)")
                 }
             }
         }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/extensions/Context.kt b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/extensions/Context.kt
index 5679bba2b..42722770b 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/extensions/Context.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/extensions/Context.kt
@@ -660,8 +660,9 @@ fun Context.getDatesWeekDateTime(date: DateTime): String {
 
 fun Context.isTaskCompleted(event: Event): Boolean {
     if (event.id == null) return false
-    val task = completedTasksDB.getTaskWithIdAndTs(event.id!!, event.startTS) ?: return false
-    return task.flags and FLAG_TASK_COMPLETED != 0
+    val originalEvent = eventsDB.getTaskWithId(event.id!!)
+    val task = completedTasksDB.getTaskWithIdAndTs(event.id!!, event.startTS)
+    return originalEvent?.isTaskCompleted() == true || task?.isTaskCompleted() == true
 }
 
 fun Context.updateTaskCompletion(event: Event, completed: Boolean) {
@@ -673,4 +674,6 @@ fun Context.updateTaskCompletion(event: Event, completed: Boolean) {
         event.flags = event.flags.removeBit(FLAG_TASK_COMPLETED)
         completedTasksDB.deleteTaskWithIdAndTs(event.id!!, event.startTS)
     }
+    // mark event as "incomplete" in the main events db
+    eventsDB.updateTaskCompletion(event.id!!, event.flags.removeBit(FLAG_TASK_COMPLETED))
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/interfaces/EventsDao.kt b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/interfaces/EventsDao.kt
index a22ad4e0c..791ec4667 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/interfaces/EventsDao.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/interfaces/EventsDao.kt
@@ -112,6 +112,10 @@ interface EventsDao {
     @Query("UPDATE events SET repetition_exceptions = :repetitionExceptions WHERE id = :id AND (type = $TYPE_EVENT OR type = $TYPE_TASK)")
     fun updateEventRepetitionExceptions(repetitionExceptions: String, id: Long)
 
+    @Deprecated("Use Context.updateTaskCompletion() instead unless you know what you are doing.")
+    @Query("UPDATE events SET flags = :newFlags WHERE id = :id")
+    fun updateTaskCompletion(id: Long, newFlags: Int)
+
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     fun insertOrUpdate(event: Event): Long
 
diff --git a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/models/Task.kt b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/models/Task.kt
index ff2cb1630..3e8ab5eaa 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calendar/pro/models/Task.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calendar/pro/models/Task.kt
@@ -4,11 +4,14 @@ import androidx.room.ColumnInfo
 import androidx.room.Entity
 import androidx.room.Index
 import androidx.room.PrimaryKey
+import com.simplemobiletools.calendar.pro.helpers.FLAG_TASK_COMPLETED
 
-@Entity(tableName = "tasks", indices = [(Index(value = ["id"], unique = true))])
+@Entity(tableName = "tasks", indices = [(Index(value = ["id", "task_id"], unique = true))])
 data class Task(
     @PrimaryKey(autoGenerate = true) var id: Long?,
     @ColumnInfo(name = "task_id") var task_id: Long,
     @ColumnInfo(name = "start_ts") var startTS: Long = 0L,
     @ColumnInfo(name = "flags") var flags: Int = 0,
-)
+) {
+    fun isTaskCompleted() = flags and FLAG_TASK_COMPLETED != 0
+}