diff --git a/config/initializers/alaveteli.rb b/config/initializers/alaveteli.rb
index 8d88ca1725..13f79e8589 100644
--- a/config/initializers/alaveteli.rb
+++ b/config/initializers/alaveteli.rb
@@ -10,7 +10,7 @@
 load "util.rb"
 
 # Application version
-ALAVETELI_VERSION = '0.40.0.1'
+ALAVETELI_VERSION = '0.40.1.0'
 
 # Add new inflection rules using the following format
 # (all these examples are active by default):
diff --git a/doc/CHANGES.md b/doc/CHANGES.md
index 7d70e0362d..53e853ef9f 100644
--- a/doc/CHANGES.md
+++ b/doc/CHANGES.md
@@ -1,3 +1,10 @@
+# 0.40.1.0
+
+## Highlighted Features
+
+* Fixes issue loading translated fields when using locales with underscores
+  (e.g. `en_RW` or `nl_BE`) (Graeme Porteous)
+
 # 0.40.0.1
 
 ## Highlighted Features
diff --git a/lib/alaveteli_localization/railtie.rb b/lib/alaveteli_localization/railtie.rb
index 280a19c829..8825fe981a 100644
--- a/lib/alaveteli_localization/railtie.rb
+++ b/lib/alaveteli_localization/railtie.rb
@@ -23,6 +23,30 @@ class Railtie < Rails::Railtie
         AlaveteliConfiguration.include_default_locale_in_urls
       )
 
+      if Rails.version < '7.0.0' && Rails.env.development?
+        ##
+        # Ideally the following would only be called in the `after_initialize`
+        # hook but this leads to an error when booting Rails 6.1 in development
+        # mode. (As config.cache_classes = false)
+        #
+        # This due Alaveteli not yet using the new Zeitwork autoloading feature
+        # and Rails attempts to render a deprecation warning which happens to
+        # includes an I18n translation so requires the default locale to be
+        # setup.
+        #
+        # Once we support Zeitwork (which is needed for Rails 7) then this can
+        # be removed.
+        #
+        # See: https://github.com/mysociety/alaveteli/issues/5382
+        #
+        AlaveteliLocalization.set_locales(
+          AlaveteliConfiguration.available_locales,
+          AlaveteliConfiguration.default_locale
+        )
+      end
+    end
+
+    config.after_initialize do
       AlaveteliLocalization.set_locales(
         AlaveteliConfiguration.available_locales,
         AlaveteliConfiguration.default_locale