diff --git a/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php b/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php
index e1ce8dc..1a24ef5 100644
--- a/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php
+++ b/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php
@@ -14,6 +14,7 @@
 use Drupal\Core\TypedData\Type\StringInterface;
 use Drupal\Core\TypedData\Type\FloatInterface;
 use Drupal\Core\TypedData\Type\IntegerInterface;
+use Drupal\Component\Utility\SafeStringInterface;
 
 /**
  * Provides a trait for checking configuration schema.
@@ -127,6 +128,11 @@ protected function checkValue($key, $value) {
       }
       // Recurse into any nested keys.
       foreach ($value as $nested_value_key => $nested_value) {
+        // We cast safe strings to a string here so as to not recurse into
+        // the safe string object itself.
+        if ($nested_value instanceof SafeStringInterface) {
+          $nested_value = (string) $nested_value;
+        }
         $errors = array_merge($errors, $this->checkValue($key . '.' . $nested_value_key, $nested_value));
       }
       return $errors;
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/BooleanItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/BooleanItem.php
index 7107436..34ebe4a 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/BooleanItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/BooleanItem.php
@@ -12,6 +12,7 @@
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\Core\TypedData\OptionsProviderInterface;
 use Drupal\Core\TypedData\DataDefinition;
 
@@ -33,8 +34,8 @@ class BooleanItem extends FieldItemBase implements OptionsProviderInterface {
    */
   public static function defaultFieldSettings() {
     return array(
-      'on_label' => t('On'),
-      'off_label' => t('Off'),
+      'on_label' => new TranslationWrapper('On'),
+      'off_label' => new TranslationWrapper('Off'),
     ) + parent::defaultFieldSettings();
   }