diff --git a/unique_field.module b/unique_field.module
--- a/unique_field.module	(revision c5406e483c36a227ab811763cbac26e8de6bc019)
+++ b/unique_field.module	(date 1779681086617)
@@ -14,13 +14,6 @@
 use Drupal\unique_field\Event\UniqueFieldTermEvent;
 use Drupal\unique_field\Event\UniqueFieldUserEvent;
 
-/**
- * The default warning message.
- *
- * @var string
- */
-const DEFAULT_WARNING_MESSAGE = 'The field @label has to be unique.';
-
 /**
  * Implements hook_help().
  */
@@ -291,7 +284,7 @@
   $title = $form_state->getValues()['title'][0]['value'];
   $langcode = $form_state->getValues()['langcode'][0]['value'];
   $node = \Drupal::routeMatch()->getParameter('node');
-  $unique_error_message = $config->get('unique_field_warnings') ? $config->get('unique_field_warnings')['node']: DEFAULT_WARNING_MESSAGE;
+  $unique_error_message = $config->get('unique_field_warnings')['node'];
 
   if ($comp_type == 'all') {
     $query = \Drupal::database()->select('node_field_data', 'n');
@@ -438,7 +431,7 @@
   }
   $scope = $config->get('unique_field_taxonomy.' . $form['#bundle'] . '.scope');
   $comp_type = $config->get('unique_field_taxonomy.' . $form['#bundle'] . '.comp');
-  $unique_error_message = $config->get('unique_field_warnings') ? $config->get('unique_field_warnings')['term']: DEFAULT_WARNING_MESSAGE;
+  $unique_error_message = $config->get('unique_field_warnings')['term'];
   $name = $form_state->getValues()['name'][0]['value'];
   $langcode = $form_state->getValues()['langcode'][0]['value'];
   $description = $form_state->getValues()['description'][0]['value'] ?? '';
@@ -589,7 +582,7 @@
   // Load the current user being edited.
   $uid = $form_state->getFormObject()->getEntity()->id();
   $comp_type = $config->get('unique_field_user.comp');
-  $unique_error_message = $config->get('unique_field_warnings') ? $config->get('unique_field_warnings')['user']: DEFAULT_WARNING_MESSAGE;
+  $unique_error_message = $config->get('unique_field_warnings')['user'];
   if ($comp_type == 'all') {
     $query = \Drupal::database()->select('users_field_data', 'u');
     $query->fields('n', ['nid']);
Index: unique_field.install
diff --git a/unique_field.install b/unique_field.install
new file mode 100644
--- /dev/null	(date 1779682408522)
+++ b/unique_field.install	(date 1779682408522)
@@ -0,0 +1,20 @@
+<?php
+
+/**
+ * @file
+ * Install hook for the Unique Field module.
+ */
+
+/**
+ * Add unique_field_warnings to the default configuration.
+ */
+function unique_field_update_8200(): void {
+  $config_factory = \Drupal::configFactory();
+  $config = $config_factory->getEditable('unique_field.settings');
+
+  $unique_field_warnings = array_map(
+    fn($warning): string => $warning ?: 'The field @label has to be unique.', $config->get('unique_field_warnings')
+  );
+
+  $config->set('unique_field_warnings', $unique_field_warnings)->save();
+}
diff --git a/config/install/unique_field.settings.yml b/config/install/unique_field.settings.yml
new file mode 100644
--- /dev/null	(date 1779680102221)
+++ b/config/install/unique_field.settings.yml	(date 1779680102221)
@@ -0,0 +1,4 @@
+unique_field_warnings:
+  node: 'The field @label has to be unique.'
+  term: 'The field @label has to be unique.'
+  user: 'The field @label has to be unique.'