diff --git a/app/src/main/java/org/tasks/caldav/iCalendar.kt b/app/src/main/java/org/tasks/caldav/iCalendar.kt
index 59a752225..95fbb07a8 100644
--- a/app/src/main/java/org/tasks/caldav/iCalendar.kt
+++ b/app/src/main/java/org/tasks/caldav/iCalendar.kt
@@ -248,7 +248,7 @@ class iCalendar @Inject constructor(
             }
         }
 
-        private val IS_APPLE_SORT_ORDER = { x: Property? -> x?.name.equals(APPLE_SORT_ORDER, true) }
+        internal val IS_APPLE_SORT_ORDER = { x: Property? -> x?.name.equals(APPLE_SORT_ORDER, true) }
         private val IS_OC_HIDESUBTASKS = { x: Property? -> x?.name.equals(OC_HIDESUBTASKS, true) }
         private val IS_MOZ_SNOOZE_TIME = { x: Property? -> x?.name.equals(MOZ_SNOOZE_TIME, true) }
         private val IS_MOZ_LASTACK = { x: Property? -> x?.name.equals(MOZ_LASTACK, true) }
diff --git a/app/src/test/java/org/tasks/caldav/extensions/XPropTests.kt b/app/src/test/java/org/tasks/caldav/extensions/XPropTests.kt
new file mode 100644
index 000000000..ac4669493
--- /dev/null
+++ b/app/src/test/java/org/tasks/caldav/extensions/XPropTests.kt
@@ -0,0 +1,38 @@
+package org.tasks.caldav.extensions
+
+import at.bitfire.ical4android.Task
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+import org.tasks.caldav.iCalendar.Companion.IS_APPLE_SORT_ORDER
+import org.tasks.caldav.iCalendar.Companion.order
+
+class XPropTests {
+    @Test
+    fun setSortOrder() {
+        val task = Task()
+        task.order = 12345
+
+        assertEquals(12345L, task.order)
+    }
+
+    @Test
+    fun removeSortOrder() {
+        val task = Task()
+        task.order = 12345
+        task.order = null
+
+        assertNull(task.order)
+        assertEquals(0, task.unknownProperties.count(IS_APPLE_SORT_ORDER))
+    }
+
+    @Test
+    fun overwriteSortOrder() {
+        val task = Task()
+        task.order = 12345
+        task.order = 67890
+
+        assertEquals(67890L, task.order)
+        assertEquals(1, task.unknownProperties.count(IS_APPLE_SORT_ORDER))
+    }
+}
\ No newline at end of file