diff --git a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt
index eb13d1d8..5199c936 100644
--- a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt
@@ -199,6 +199,7 @@ class ThreadActivity : SimpleActivity() {
             R.id.block_number -> blockNumber()
             R.id.delete -> askConfirmDelete()
             R.id.manage_people -> managePeople()
+            R.id.mark_as_unread -> markAsUnread()
             else -> return super.onOptionsItemSelected(item)
         }
         return true
@@ -392,6 +393,16 @@ class ThreadActivity : SimpleActivity() {
         showSelectedContacts()
     }
 
+    private fun markAsUnread() {
+        ensureBackgroundThread {
+            conversationsDB.markUnread(threadId.toLong())
+            markThreadMessagesUnread(threadId)
+            runOnUiThread {
+                finish()
+            }
+        }
+    }
+
     @SuppressLint("MissingPermission")
     private fun getThreadItems(): ArrayList<ThreadItem> {
         messages.sortBy { it.date }
diff --git a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/Context.kt b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/Context.kt
index d534d4c4..6631484e 100644
--- a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/Context.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/extensions/Context.kt
@@ -511,6 +511,18 @@ fun Context.markThreadMessagesRead(threadId: Int) {
     }
 }
 
+fun Context.markThreadMessagesUnread(threadId: Int) {
+    arrayOf(Mms.CONTENT_URI, Sms.CONTENT_URI).forEach { uri ->
+        val contentValues = ContentValues().apply {
+            put(Sms.READ, 0)
+            put(Sms.SEEN, 0)
+        }
+        val selection = "${Sms.THREAD_ID} = ?"
+        val selectionArgs = arrayOf(threadId.toString())
+        contentResolver.update(uri, contentValues, selection, selectionArgs)
+    }
+}
+
 @SuppressLint("NewApi")
 fun Context.getThreadId(address: String): Long {
     return if (isMarshmallowPlus()) {
diff --git a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/interfaces/ConversationsDao.kt b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/interfaces/ConversationsDao.kt
index 422245ce..72d69763 100644
--- a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/interfaces/ConversationsDao.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/interfaces/ConversationsDao.kt
@@ -17,6 +17,9 @@ interface ConversationsDao {
     @Query("UPDATE conversations SET read = 1 WHERE thread_id = :threadId")
     fun markRead(threadId: Long)
 
+    @Query("UPDATE conversations SET read = 0 WHERE thread_id = :threadId")
+    fun markUnread(threadId: Long)
+
     @Query("DELETE FROM conversations WHERE id = :id")
     fun delete(id: Long)
 
diff --git a/app/src/main/res/menu/menu_thread.xml b/app/src/main/res/menu/menu_thread.xml
index 4787cb75..2a1ecf93 100644
--- a/app/src/main/res/menu/menu_thread.xml
+++ b/app/src/main/res/menu/menu_thread.xml
@@ -16,4 +16,8 @@
         android:icon="@drawable/ic_block_vector"
         android:title="@string/block_number"
         app:showAsAction="never" />
+    <item
+        android:id="@+id/mark_as_unread"
+        android:title="@string/mark_as_unread"
+        app:showAsAction="never" />
 </menu>