diff --git a/app/models/account_conversation.rb b/app/models/account_conversation.rb
index b7447d805..cc6b39279 100644
--- a/app/models/account_conversation.rb
+++ b/app/models/account_conversation.rb
@@ -58,6 +58,9 @@ class AccountConversation < ApplicationRecord
 
     def add_status(recipient, status)
       conversation = find_or_initialize_by(account: recipient, conversation_id: status.conversation_id, participant_account_ids: participants_from_status(recipient, status))
+
+      return conversation if conversation.status_ids.include?(status.id)
+
       conversation.status_ids << status.id
       conversation.unread = status.account_id != recipient.id
       conversation.save
diff --git a/db/migrate/20181024224956_migrate_account_conversations.rb b/db/migrate/20181024224956_migrate_account_conversations.rb
new file mode 100644
index 000000000..1821e8c27
--- /dev/null
+++ b/db/migrate/20181024224956_migrate_account_conversations.rb
@@ -0,0 +1,43 @@
+class MigrateAccountConversations < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def up
+    say ''
+    say 'WARNING: This migration may take a *long* time for large instances'
+    say 'It will *not* lock tables for any significant time, but it may run'
+    say 'for a very long time. We will pause for 10 seconds to allow you to'
+    say 'interrupt this migration if you are not ready.'
+    say ''
+
+    10.downto(1) do |i|
+      say "Continuing in #{i} second#{i == 1 ? '' : 's'}...", true
+      sleep 1
+    end
+
+    local_direct_statuses.find_each do |status|
+      AccountConversation.add_status(status.account, status)
+    end
+
+    notifications_about_direct_statuses.find_each do |notification|
+      AccountConversation.add_status(notification.account, notification.target_status)
+    end
+  end
+
+  def down
+  end
+
+  private
+
+  def local_direct_statuses
+    Status.unscoped
+          .local
+          .where(visibility: :direct)
+          .includes(:account, mentions: :account)
+  end
+
+  def notifications_about_direct_statuses
+    Notification.joins(mention: :status)
+                .where(activity_type: 'Mention', statuses: { visibility: :direct })
+                .includes(:account, mention: { status: [:account, mentions: :account] })
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 8facfa259..3c4f41648 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2018_10_18_205649) do
+ActiveRecord::Schema.define(version: 2018_10_24_224956) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"