diff --git a/core/modules/options/lib/Drupal/options/Plugin/field/field_type/ListItemBase.php b/core/modules/options/lib/Drupal/options/Plugin/field/field_type/ListItemBase.php
index bfe126c..3d116a6 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/field/field_type/ListItemBase.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/field/field_type/ListItemBase.php
@@ -136,7 +136,7 @@ public function validateAllowedValues($element, &$form_state) {
 
       // Prevent removing values currently in use.
       if ($has_data) {
-        $lost_keys = array_diff(array_keys($field['settings']['allowed_values']), array_keys($values));
+        $lost_keys = array_diff(array_keys($field->getFieldSetting('allowed_values')), array_keys($values));
         if (_options_values_in_use($field, $lost_keys)) {
           form_error($element, t('Allowed values list: some values are being removed while currently in use.'));
         }
@@ -246,8 +246,8 @@ public function getConstraints() {
       'value' => array(
         'Choice' => array(
           'choices' => array_keys($allowed_values),
-          'message' => t('%name: illegal value.', array('%name' => $instance['label'])),
-          'multiple' => $instance->getFieldCardinality() == FIELD_CARDINALITY_UNLIMITED,
+          'message' => t('%name: illegal value selected.', array('%name' => $instance['label'])),
+          'multiple' => $instance->getFieldCardinality() != 1,
         ),
       ),
     ));