diff --git a/app/models/topic.rb b/app/models/topic.rb
index 19a3da5902e..4e160b6b3a4 100644
--- a/app/models/topic.rb
+++ b/app/models/topic.rb
@@ -231,10 +231,19 @@ class Topic < ActiveRecord::Base
     posts.order('score desc').limit(1).first
   end
 
+  def has_flags?
+    FlagQuery.flagged_post_actions("active")
+             .where("topics.id" => id)
+             .exists?
+  end
+
   # all users (in groups or directly targetted) that are going to get the pm
   def all_allowed_users
-    # TODO we should probably change this from 3 queries to 1
-    User.where('id in (?)', allowed_users.select('users.id').to_a + allowed_group_users.select('users.id').to_a)
+    # TODO we should probably change this to 1 query
+    allowed_user_ids = allowed_users.select('users.id').to_a
+    allowed_group_user_ids = allowed_group_users.select('users.id').to_a
+    allowed_staff_ids = private_message? && has_flags? ? User.where(moderator: true).pluck(:id).to_a : []
+    User.where('id IN (?)', allowed_user_ids + allowed_group_user_ids + allowed_staff_ids)
   end
 
   # Additional rate limits on topics: per day and private messages per day
diff --git a/lib/flag_query.rb b/lib/flag_query.rb
index 2fe90c1c195..aed258c8274 100644
--- a/lib/flag_query.rb
+++ b/lib/flag_query.rb
@@ -6,7 +6,9 @@ module FlagQuery
     guardian = Guardian.new(current_user)
 
     if !guardian.is_admin?
-      actions = actions.where('category_id in (?)', guardian.allowed_category_ids)
+      actions = actions.where('category_id IN (:allowed_category_ids) OR archetype = :private_message',
+        allowed_category_ids: guardian.allowed_category_ids,
+        private_message: Archetype.private_message)
     end
 
     post_ids = actions.limit(per_page)
@@ -107,26 +109,24 @@ module FlagQuery
     ]
   end
 
-  protected
-
-    def self.flagged_post_actions(filter)
-      post_actions = PostAction.flags
-                               .joins("INNER JOIN posts ON posts.id = post_actions.post_id")
-                               .joins("INNER JOIN topics ON topics.id = posts.topic_id")
-                               .joins("LEFT JOIN users ON users.id = posts.user_id")
-
-      if filter == "old"
-        post_actions.where("post_actions.disagreed_at IS NOT NULL OR
-                            post_actions.deferred_at IS NOT NULL OR
-                            post_actions.agreed_at IS NOT NULL")
-      else
-        post_actions.active
-                    .where("posts.deleted_at" => nil)
-                    .where("topics.deleted_at" => nil)
-      end
+  def self.flagged_post_actions(filter)
+    post_actions = PostAction.flags
+                             .joins("INNER JOIN posts ON posts.id = post_actions.post_id")
+                             .joins("INNER JOIN topics ON topics.id = posts.topic_id")
+                             .joins("LEFT JOIN users ON users.id = posts.user_id")
 
+    if filter == "old"
+      post_actions.where("post_actions.disagreed_at IS NOT NULL OR
+                          post_actions.deferred_at IS NOT NULL OR
+                          post_actions.agreed_at IS NOT NULL")
+    else
+      post_actions.active
+                  .where("posts.deleted_at" => nil)
+                  .where("topics.deleted_at" => nil)
     end
 
+  end
+
   private
 
     def self.excerpt(cooked)
diff --git a/spec/components/guardian_spec.rb b/spec/components/guardian_spec.rb
index 2a6318ab9d8..e39f46b838f 100644
--- a/spec/components/guardian_spec.rb
+++ b/spec/components/guardian_spec.rb
@@ -381,6 +381,19 @@ describe Guardian do
         expect(Guardian.new(moderator).can_edit?(tos_topic)).to be_falsey
         expect(Guardian.new(admin).can_edit?(tos_topic)).to be_truthy
       end
+
+      it "allows moderators to see a flagged private message" do
+        moderator.save!
+        user.save!
+
+        private_topic = Fabricate(:private_message_topic, user: user)
+        first_post = Fabricate(:post, topic: private_topic, user: user)
+
+        expect(Guardian.new(moderator).can_see?(private_topic)).to be_falsey
+
+        PostAction.act(user, first_post, PostActionType.types[:off_topic])
+        expect(Guardian.new(moderator).can_see?(private_topic)).to be_truthy
+      end
     end
 
     describe 'a Post' do