diff --git a/app/models/post_action.rb b/app/models/post_action.rb
index dcac3b290e5..c7d28f810fe 100644
--- a/app/models/post_action.rb
+++ b/app/models/post_action.rb
@@ -89,6 +89,9 @@ class PostAction < ActiveRecord::Base
     I18n.with_locale(SiteSetting.default_locale) do
       related_post.topic.add_moderator_post(moderator, I18n.t(message_key))
     end
+
+    # archive message for moderators
+    GroupArchivedMessage.archive!(Group[:moderators].id, related_post.topic)
   end
 
   def staff_already_replied?(topic)
diff --git a/spec/models/post_action_spec.rb b/spec/models/post_action_spec.rb
index 26df835d891..dc71f1e001f 100644
--- a/spec/models/post_action_spec.rb
+++ b/spec/models/post_action_spec.rb
@@ -88,6 +88,7 @@ describe PostAction do
       topic.reload
       expect(topic.posts.count).to eq(2)
       expect(topic.posts.last.post_type).to eq(Post.types[:moderator_action])
+      expect(topic.message_archived?(mod)).to eq(true)
     end
 
   end