diff --git a/lib/post_destroyer.rb b/lib/post_destroyer.rb
index 82aa4d658..68ae562a1 100644
--- a/lib/post_destroyer.rb
+++ b/lib/post_destroyer.rb
@@ -5,8 +5,22 @@
 class PostDestroyer
 
   def self.destroy_stubs
+    # exclude deleted topics and posts that are actively flagged
     Post.where(deleted_at: nil, user_deleted: true)
-        .where('updated_at < ? AND post_number > 1', 1.day.ago).each do |post|
+        .where("NOT EXISTS (
+            SELECT 1 FROM topics t
+            WHERE t.deleted_at IS NOT NULL AND
+                  t.id = posts.topic_id
+        )")
+        .where("updated_at < ? AND post_number > 1", 1.day.ago)
+        .where("NOT EXISTS (
+                  SELECT 1
+                  FROM post_actions pa
+                  WHERE pa.post_id = posts.id AND
+                        pa.deleted_at IS NULL AND
+                        pa.post_action_type_id IN (?)
+              )", PostActionType.notify_flag_type_ids)
+        .each do |post|
       PostDestroyer.new(Discourse.system_user, post).destroy
     end
   end
@@ -39,6 +53,9 @@ class PostDestroyer
   # When a post is properly deleted. Well, it's still soft deleted, but it will no longer
   # show up in the topic
   def staff_destroyed
+    # the topic may be trashed, skip it
+    return unless @post.topic
+
     Post.transaction do
 
       # Update the last post id to the previous post if it exists
diff --git a/spec/components/post_destroyer_spec.rb b/spec/components/post_destroyer_spec.rb
index d38c9d1fc..5a404d59b 100644
--- a/spec/components/post_destroyer_spec.rb
+++ b/spec/components/post_destroyer_spec.rb
@@ -13,9 +13,10 @@ describe PostDestroyer do
   describe 'destroy_old_stubs' do
     it 'destroys stubs for deleted by user posts' do
       Fabricate(:admin)
-      reply1 = create_post(topic: post.topic)
-      reply2 = create_post(topic: post.topic)
-      reply3 = create_post(topic: post.topic)
+      topic = post.topic
+      reply1 = create_post(topic: topic)
+      reply2 = create_post(topic: topic)
+      reply3 = create_post(topic: topic)
 
       PostDestroyer.new(reply1.user, reply1).destroy
       PostDestroyer.new(reply2.user, reply2).destroy
@@ -32,6 +33,24 @@ describe PostDestroyer do
       reply2.deleted_at.should_not == nil
       reply3.deleted_at.should == nil
 
+      # if topic is deleted we should still be able to destroy stubs
+
+      topic.trash!
+      reply1.update_column(:updated_at, 2.days.ago)
+      PostDestroyer.destroy_stubs
+
+      reply1.reload
+      reply1.deleted_at.should == nil
+
+      # flag the post, it should not nuke the stub anymore
+      topic.recover!
+      PostAction.act(Fabricate(:coding_horror), reply1, PostActionType.types[:spam])
+
+      PostDestroyer.destroy_stubs
+
+      reply1.reload
+      reply1.deleted_at.should == nil
+
     end
   end