diff --git a/app/models/procedure.rb b/app/models/procedure.rb
index a2912b7b6..3a6c9e652 100644
--- a/app/models/procedure.rb
+++ b/app/models/procedure.rb
@@ -43,7 +43,6 @@
 #  published_revision_id               :bigint
 #  service_id                          :bigint
 #
-require Rails.root.join('lib', 'percentile')
 
 class Procedure < ApplicationRecord
   self.ignored_columns = ['archived_at', 'csv_export_queued', 'xlsx_export_queued', 'ods_export_queued']
diff --git a/config/application.rb b/config/application.rb
index cc8508f4f..ab6c2cf5e 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -17,9 +17,10 @@ module TPS
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.
 
-    # The default autoloader since Rails 6.0 defaults is zeitwerk.
-    # However, to split the work, we will move to zeitwerk only in a future PR.
-    config.autoloader = :classic
+    Rails.autoloaders.main.ignore(Rails.root.join('lib/cops'))
+    Rails.autoloaders.main.ignore(Rails.root.join('lib/linters'))
+    Rails.autoloaders.main.ignore(Rails.root.join('lib/tasks/task_helper.rb'))
+    config.paths.add Rails.root.join('spec/mailers/previews').to_s, eager_load: true
 
     # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
     # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
diff --git a/config/initializers/core_ext.rb b/config/initializers/core_ext.rb
new file mode 100644
index 000000000..99b320fcd
--- /dev/null
+++ b/config/initializers/core_ext.rb
@@ -0,0 +1,3 @@
+Dir[File.join(Rails.root, "lib", "core_ext", "*.rb")].each do |core_ext_file|
+  require core_ext_file
+end
diff --git a/lib/percentile.rb b/lib/core_ext/array.rb
similarity index 100%
rename from lib/percentile.rb
rename to lib/core_ext/array.rb