diff --git a/config/schema/extlink.schema.yml b/config/schema/extlink.schema.yml
index d4f7b60..b8197a1 100644
--- a/config/schema/extlink.schema.yml
+++ b/config/schema/extlink.schema.yml
@@ -26,7 +26,7 @@ extlink.settings:
       type: string
       label: 'Include links matching the pattern'
     extlink_class:
-      type: string
+      type: varchar
       label: 'Add icon to external links'
     extlink_label:
       type: label
diff --git a/extlink.install b/extlink.install
index 1d1c385..ee56d97 100644
--- a/extlink.install
+++ b/extlink.install
@@ -23,3 +23,13 @@ function extlink_update_8101() {
   $config->set('extlink_mailto_label', '(link sends email)');
   $config->save(TRUE);
 }
+
+/**
+ * Add extlink class to the default configuration.
+ */
+function extlink_update_8102() {
+  // Update schema
+  \Drupal::configFactory()->getEditable('extlink.settings')
+    ->set('extlink_class', 'ext')
+    ->save();
+}
diff --git a/src/Form/ExtlinkAdminSettingsForm.php b/src/Form/ExtlinkAdminSettingsForm.php
index 52d6b39..7241c05 100644
--- a/src/Form/ExtlinkAdminSettingsForm.php
+++ b/src/Form/ExtlinkAdminSettingsForm.php
@@ -190,7 +190,7 @@ class ExtlinkAdminSettingsForm extends ConfigFormBase {
       ->set('extlink_subdomains', $values['extlink_subdomains'])
       ->set('extlink_mailto_class', $values['extlink_mailto_class'])
       ->set('extlink_img_class', $values['extlink_img_class'])
-      ->set('extlink_class', $values['extlink_class'])
+      ->set('extlink_class', ($values['extlink_class'] === '0') ? (int) $values['extlink_class'] : $values['extlink_class'])
       ->set('extlink_css_exclude', $values['extlink_css_exclude'])
       ->set('extlink_css_explicit', $values['extlink_css_explicit'])
       ->save();