diff --git a/src/ElasticSearch/Parameters/Factory/IndexFactory.php b/src/ElasticSearch/Parameters/Factory/IndexFactory.php
index 4991e4a..f3fdb28 100644
--- a/src/ElasticSearch/Parameters/Factory/IndexFactory.php
+++ b/src/ElasticSearch/Parameters/Factory/IndexFactory.php
@@ -4,6 +4,8 @@ namespace Drupal\elasticsearch_connector\ElasticSearch\Parameters\Factory;

 use Drupal\elasticsearch_connector\Event\PrepareDocumentIndexEvent;
 use Drupal\search_api\IndexInterface;
+use Drupal\search_api\Utility\Utility;
+use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\elasticsearch_connector\Event\PrepareIndexEvent;
 use Drupal\elasticsearch_connector\Event\PrepareIndexMappingEvent;
 use Drupal\search_api_autocomplete\Suggester\SuggesterInterface;
@@ -120,12 +122,24 @@ class IndexFactory {
       /** @var \Drupal\search_api\Item\FieldInterface $field */
       foreach ($item as $name => $field) {
         $field_type = $field->getType();
-        $values = [];
+
+        // Set to list only if list.
+        $value = NULL;
+        if (self::isFieldList($index, $field)) {
+          $value = [];
+        }
+
         if (!empty($field->getValues())) {
-          foreach ($field->getValues() as $value) {
-            $values[] = self::getFieldValue($field_type, $value);
+          foreach ($field->getValues() as $val) {
+            if (self::isFieldList($index, $field)) {
+              $value[] = self::getFieldValue($field_type, $val);
+            }
+            else {
+              $value = self::getFieldValue($field_type, $val);
+            }
           }
-          $data[$field->getFieldIdentifier()] = $values;
+
+          $data[$field->getFieldIdentifier()] = $value;
         }
       }
       // Allow other modules to alter document before we create it.
@@ -299,4 +313,35 @@ class IndexFactory {
     return $value;
   }

+  /**
+   * Helper function. Returns true if the field is a list of values.
+   *
+   * @param \Drupal\search_api\IndexInterface $index
+   * @param \Drupal\search_api\Item\Field $field
+   *
+   * @return bool
+   */
+  protected static function isFieldList($index, $field) {
+    $is_list = FALSE;
+
+    // Ensure we get the field definition for the root/parent field item (ie tags).
+    $property_definitions =  $index->getPropertyDefinitions($field->getDatasourceId());
+    $root_property = Utility::splitPropertyPath($field->getPropertyPath(), FALSE)[0];
+    $field_definition = $property_definitions[$root_property];
+
+    // Using $field_definition->isList() doesn't seem to be accurate, so we
+    // check the fieldStorage cardinality !=1.
+    if ($field_definition instanceof FieldDefinitionInterface) {
+      $storage = $field_definition->getFieldStorageDefinition();
+      if (1 != $storage->getCardinality()) {
+        $is_list = TRUE;
+      }
+    }
+    else {
+      $is_list = $field_definition->isList();
+    }
+
+    return $is_list;
+  }
+
 }