diff --git a/db/migrate/20170918125918_ids_to_bigints.rb b/db/migrate/20170918125918_ids_to_bigints.rb
index bf875e4e5..e3fc34a51 100644
--- a/db/migrate/20170918125918_ids_to_bigints.rb
+++ b/db/migrate/20170918125918_ids_to_bigints.rb
@@ -1,7 +1,9 @@
-require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+require_relative '../../lib/mastodon/migration_helpers'
+require_relative '../../lib/mastodon/migration_warning'
 
 class IdsToBigints < ActiveRecord::Migration[5.1]
   include Mastodon::MigrationHelpers
+  include Mastodon::MigrationWarning
 
   disable_ddl_transaction!
 
@@ -69,24 +71,12 @@ class IdsToBigints < ActiveRecord::Migration[5.1]
     ]
     included_columns << [:deprecated_preview_cards, :id] if table_exists?(:deprecated_preview_cards)
 
-    # Print out a warning that this will probably take a while.
-    if $stdout.isatty
-      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 ''
-      say 'This migration has some sections that can be safely interrupted'
-      say 'and restarted later, and will tell you when those are occurring.'
-      say ''
-      say 'For more information, see https://github.com/mastodon/mastodon/pull/5088'
+    migration_duration_warning(<<~EXPLANATION)
+      This migration has some sections that can be safely interrupted
+      and restarted later, and will tell you when those are occurring.
 
-      10.downto(1) do |i|
-        say "Continuing in #{i} second#{i == 1 ? '' : 's'}...", true
-        sleep 1
-      end
-    end
+      For more information, see https://github.com/mastodon/mastodon/pull/5088
+    EXPLANATION
 
     tables = included_columns.map(&:first).uniq
     table_sizes = {}
diff --git a/db/migrate/20180528141303_fix_accounts_unique_index.rb b/db/migrate/20180528141303_fix_accounts_unique_index.rb
index 0b39f7107..1e67b4bb4 100644
--- a/db/migrate/20180528141303_fix_accounts_unique_index.rb
+++ b/db/migrate/20180528141303_fix_accounts_unique_index.rb
@@ -1,4 +1,8 @@
+require_relative '../../lib/mastodon/migration_warning'
+
 class FixAccountsUniqueIndex < ActiveRecord::Migration[5.2]
+  include Mastodon::MigrationWarning
+
   class Account < ApplicationRecord
     # Dummy class, to make migration possible across version changes
     has_one :user, inverse_of: :account
@@ -35,22 +39,11 @@ class FixAccountsUniqueIndex < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def up
-    if $stdout.isatty
-      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 ''
-      say 'This migration will irreversibly delete user accounts with duplicate'
-      say 'usernames. You may use the `rake mastodon:maintenance:find_duplicate_usernames`'
-      say 'task to manually deal with such accounts before running this migration.'
-
-      10.downto(1) do |i|
-        say "Continuing in #{i} second#{i == 1 ? '' : 's'}...", true
-        sleep 1
-      end
-    end
+    migration_duration_warning(<<~EXPLANATION)
+      This migration will irreversibly delete user accounts with duplicate
+      usernames. You may use the `rake mastodon:maintenance:find_duplicate_usernames`
+      task to manually deal with such accounts before running this migration.
+    EXPLANATION
 
     duplicates = Account.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM accounts GROUP BY lower(username), lower(domain) HAVING count(*) > 1').to_ary
 
diff --git a/db/migrate/20181024224956_migrate_account_conversations.rb b/db/migrate/20181024224956_migrate_account_conversations.rb
index aca6638e1..e4dcdb18b 100644
--- a/db/migrate/20181024224956_migrate_account_conversations.rb
+++ b/db/migrate/20181024224956_migrate_account_conversations.rb
@@ -1,4 +1,8 @@
+require_relative '../../lib/mastodon/migration_warning'
+
 class MigrateAccountConversations < ActiveRecord::Migration[5.2]
+  include Mastodon::MigrationWarning
+
   disable_ddl_transaction!
 
   class Mention < ApplicationRecord
@@ -62,19 +66,7 @@ class MigrateAccountConversations < ActiveRecord::Migration[5.2]
   end
 
   def up
-    if $stdout.isatty
-      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
-    end
+    migration_duration_warning
 
     migrated  = 0
     last_time = Time.zone.now
diff --git a/lib/mastodon/migration_warning.rb b/lib/mastodon/migration_warning.rb
new file mode 100644
index 000000000..227f6705d
--- /dev/null
+++ b/lib/mastodon/migration_warning.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module Mastodon
+  module MigrationWarning
+    WARNING_SECONDS = 10
+
+    DEFAULT_WARNING = <<~WARNING_MESSAGE
+      WARNING: This migration may take a *long* time for large instances.
+      It will *not* lock tables for any significant time, but it may run
+      for a very long time. We will pause for #{WARNING_SECONDS} seconds to allow you to
+      interrupt this migration if you are not ready.
+    WARNING_MESSAGE
+
+    def migration_duration_warning(explanation = nil)
+      return unless valid_environment?
+
+      announce_warning(explanation)
+
+      announce_countdown
+    end
+
+    private
+
+    def announce_countdown
+      WARNING_SECONDS.downto(1) do |i|
+        say "Continuing in #{i} second#{i == 1 ? '' : 's'}...", true
+        sleep 1
+      end
+    end
+
+    def valid_environment?
+      $stdout.isatty && Rails.env.production?
+    end
+
+    def announce_warning(explanation)
+      announce_message prepare_message(explanation)
+    end
+
+    def announce_message(text)
+      say ''
+      text.each_line do |line|
+        say(line)
+      end
+      say ''
+    end
+
+    def prepare_message(explanation)
+      if explanation.blank?
+        DEFAULT_WARNING
+      else
+        DEFAULT_WARNING + "\n#{explanation}"
+      end
+    end
+  end
+end