diff --git a/src/Plugin/search_api/processor/AddHierarchy.php b/src/Plugin/search_api/processor/AddHierarchy.php
index b6f4bb8..9e73d14 100644
--- a/src/Plugin/search_api/processor/AddHierarchy.php
+++ b/src/Plugin/search_api/processor/AddHierarchy.php
@@ -77,11 +77,12 @@ public function setEntityTypeManager(EntityTypeManagerInterface $entity_type_man
    * {@inheritdoc}
    */
   public static function supportsIndex(IndexInterface $index) {
-    return (bool) static::getHierarchyFields($index);
+    $processor = new static(array('#index' => $index), 'hierarchy', array());
+    return (bool) $processor->getHierarchyFields();
   }
 
   /**
-   * Finds all (potentially) hierarchical fields for the given index.
+   * Finds all (potentially) hierarchical fields for this processor's index.
    *
    * Fields are returned if:
    * - they point to an entity type; and
@@ -89,9 +90,6 @@ public static function supportsIndex(IndexInterface $index) {
    *   (so that a hierarchy could be built from that nested property); or
    * - that entity type has the same field.
    *
-   * @param \Drupal\search_api\IndexInterface $index
-   *   The index for which hierarchical fields should be found.
-   *
    * @return string[][]
    *   An array containing all fields of the index for which hierarchical data
    *   might be retrievable. The keys are those field's IDs, the values are
@@ -99,10 +97,10 @@ public static function supportsIndex(IndexInterface $index) {
    *   which a hierarchy might be constructed, with the property paths as the
    *   keys and labels as the values.
    */
-  protected static function getHierarchyFields(IndexInterface $index) {
+  protected function getHierarchyFields() {
     $field_options = array();
 
-    foreach ($index->getFields() as $field_id => $field) {
+    foreach ($this->index->getFields() as $field_id => $field) {
       $definition = $field->getDataDefinition();
       if ($definition instanceof ComplexDataDefinitionInterface) {
         $properties = $definition->getPropertyDefinitions();
@@ -110,9 +108,7 @@ protected static function getHierarchyFields(IndexInterface $index) {
         $properties[''] = $definition;
         foreach ($properties as $property) {
           $property_label = $property->getLabel();
-          $property = \Drupal::getContainer()
-            ->get('search_api.fields_helper')
-            ->getInnerProperty($property);
+          $property = $this->getFieldsHelper()->getInnerProperty($property);
           if ($property instanceof EntityDataDefinitionInterface) {
             $options = self::findHierarchicalProperties($property, $property_label);
             if ($options) {
@@ -152,15 +148,14 @@ protected static function getHierarchyFields(IndexInterface $index) {
    *   property's entity type ID and the nested properties identifier,
    *   concatenated with a dash (-).
    */
-  protected static function findHierarchicalProperties(EntityDataDefinitionInterface $property, $property_label) {
+  protected function findHierarchicalProperties(EntityDataDefinitionInterface $property, $property_label) {
     $entity_type_id = $property->getEntityTypeId();
     $options = array();
-    $fields_helper = \Drupal::getContainer()->get('search_api.fields_helper');
 
     // Check properties for potential hierarchy.
     foreach ($property->getPropertyDefinitions() as $name_2 => $property_2) {
       $property_2_label = $property_2->getLabel();
-      $property_2 = $fields_helper->getInnerProperty($property_2);
+      $property_2 = $this->getFieldsHelper()->getInnerProperty($property_2);
       if ($property_2 instanceof EntityDataDefinitionInterface) {
         if ($property_2->getEntityTypeId() == $entity_type_id) {
           $options["$entity_type_id-$name_2"] = Html::escape($property_label . ' » ' . $property_2_label);
@@ -168,7 +163,7 @@ protected static function findHierarchicalProperties(EntityDataDefinitionInterfa
       }
       elseif ($property_2 instanceof ComplexDataDefinitionInterface) {
         foreach ($property_2->getPropertyDefinitions() as $property_3) {
-          $property_3 = $fields_helper->getInnerProperty($property_3);
+          $property_3 = $this->getFieldsHelper()->getInnerProperty($property_3);
           if ($property_3 instanceof EntityDataDefinitionInterface) {
             if ($property_3->getEntityTypeId() == $entity_type_id) {
               $options["$entity_type_id-$name_2"] = Html::escape($property_label . ' » ' . $property_2_label);
@@ -196,7 +191,7 @@ public function defaultConfiguration() {
   public function buildConfigurationForm(array $form, FormStateInterface $formState) {
     $form['#description'] = $this->t('Select the fields to which hierarchical data should be added.');
 
-    foreach (static::getHierarchyFields($this->index) as $field_id => $options) {
+    foreach ($this->getHierarchyFields() as $field_id => $options) {
       $enabled = !empty($this->configuration['fields'][$field_id]);
       $form['fields'][$field_id]['status'] = array(
         '#type' => 'checkbox',