diff --git a/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php b/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php
index db8ba5c..d1c3cc6 100644
--- a/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php
+++ b/modules/core_search_facets/src/Plugin/facets/facet_source/CoreNodeSearchFacetSource.php
@@ -220,7 +220,8 @@ public function getFields() {
     $facet_fields = $this->getDefaultFields();
 
     // Get the allowed field types.
-    $allowed_field_types = \Drupal::moduleHandler()->invokeAll('facets_core_allowed_field_types', array($field_types = []));
+    $allowed_field_types = \Drupal::moduleHandler()
+      ->invokeAll('facets_core_allowed_field_types', [$field_types = []]);
 
     // Get the current field instances and detect if the field type is allowed.
     $fields = FieldConfig::loadMultiple();
@@ -359,7 +360,17 @@ public function calculateDependencies() {
    * {@inheritdoc}
    */
   public function getDataDefinitions() {
-    // Get and return an array field definitions.
+    $fields = $this->getFields();
+    $field_configs = FieldConfig::loadMultiple();
+    $definitions = [];
+    foreach ($field_configs as $id => $config) {
+      if (isset($fields[$config->getName()])) {
+        $definitions[] = \Drupal::typedDataManager()
+          ->getDefinition('field_item:' . $config->getFieldStorageDefinition()->getType());
+      }
+    }
+
+    return $definitions;
   }
 
 }
diff --git a/src/Plugin/facets/processor/ListItemProcessor.php b/src/Plugin/facets/processor/ListItemProcessor.php
index caf5a44..14cc0f1 100644
--- a/src/Plugin/facets/processor/ListItemProcessor.php
+++ b/src/Plugin/facets/processor/ListItemProcessor.php
@@ -180,13 +180,13 @@ public function build(FacetInterface $facet, array $results) {
    *   The changed results.
    */
   protected function overWriteDisplayValues(array $results, array $replacements) {
-    /** @var \Drupal\facets\Result\ResultInterface $a */
-    foreach ($results as &$a) {
-      if (isset($replacements[$a->getRawValue()])) {
-        $a->setDisplayValue($replacements[$a->getRawValue()]);
+    return array_map(function ($item) use ($replacements) {
+      /** @var \Drupal\facets\Result\ResultInterface $item */
+      if (isset($replacements[$item->getRawValue()])) {
+        $item->setDisplayValue($replacements[$item->getRawValue()]);
       }
-    }
-    return $results;
+      return $item;
+    }, $results);
   }
 
 }
diff --git a/tests/src/Kernel/Entity/FacetFacetSourceTest.php b/tests/src/Kernel/Entity/FacetFacetSourceTest.php
index feb62d2..7071a2b 100644
--- a/tests/src/Kernel/Entity/FacetFacetSourceTest.php
+++ b/tests/src/Kernel/Entity/FacetFacetSourceTest.php
@@ -143,15 +143,21 @@ public function testDataDefinitions() {
     $display_name = 'search_api:views_page__search_api_test_view__page_1';
     $entity->setFacetSourceId($display_name);
 
+    // Test that ::getDataDefinitions returns an array with the defined fields,
+    // check on a couple of the fields.
     $dataDefinitions = $entity->getFacetSource()->getDataDefinitions();
     $this->assertInternalType('array', $dataDefinitions);
     $this->assertArrayHasKey('name', $dataDefinitions);
     $this->assertArrayHasKey('type', $dataDefinitions);
     $this->assertArrayHasKey('category', $dataDefinitions);
+    $this->assertInstanceOf(DataDefinitionInterface::class, $dataDefinitions['name']);
+    $this->assertInstanceOf(DataDefinitionInterface::class, $dataDefinitions['type']);
+    $this->assertInstanceOf(DataDefinitionInterface::class, $dataDefinitions['category']);
 
+    // Check the return value of ::getDataDefinition.
     $this->assertInstanceOf(DataDefinitionInterface::class, $entity->getFacetSource()->getDataDefinition('id'));
 
-    // When giving a field that doesn't exist, we should throw an error.
+    // When trying to get a field that doesn't exist, an error should be thrown.
     $this->setExpectedException(Exception::class);
     $entity->getFacetSource()->getDataDefinition('llama');
   }