diff --git a/lib/post_creator.rb b/lib/post_creator.rb
index 2d54204d9..13e23d22d 100644
--- a/lib/post_creator.rb
+++ b/lib/post_creator.rb
@@ -265,7 +265,11 @@ class PostCreator
     return unless @topic.private_message?
 
     unless @topic.topic_allowed_users.where(user_id: @user.id).exists?
-      @topic.topic_allowed_users.create!(user_id: @user.id)
+      unless @topic.topic_allowed_groups.where('group_id IN (
+                                              SELECT group_id FROM group_users where user_id = ?
+                                           )',@user.id).exists?
+        @topic.topic_allowed_users.create!(user_id: @user.id)
+      end
     end
   end
 
diff --git a/spec/components/post_creator_spec.rb b/spec/components/post_creator_spec.rb
index 958cdbd8e..b3195b3c5 100644
--- a/spec/components/post_creator_spec.rb
+++ b/spec/components/post_creator_spec.rb
@@ -490,6 +490,16 @@ describe PostCreator do
       expect(post.topic.topic_allowed_users.where(user_id: admin.id).count).to eq(1)
 
       expect(UserArchivedMessage.where(user_id: target_user2.id, topic_id: post.topic_id).count).to eq(0)
+
+      # if another admin replies and is already member of the group, don't add them to topic_allowed_users
+      group = Fabricate(:group)
+      post.topic.topic_allowed_groups.create!(group: group)
+      admin2 = Fabricate(:admin)
+      group.add(admin2)
+
+      PostCreator.create(admin2, raw: 'I am also an admin, and a mod', topic_id: post.topic_id)
+
+      expect(post.topic.topic_allowed_users.where(user_id: admin2.id).count).to eq(0)
     end
   end