diff --git a/search_api_db/tests/src/Kernel/BackendTest.php b/search_api_db/tests/src/Kernel/BackendTest.php
index 3f5146c..a294032 100644
--- a/search_api_db/tests/src/Kernel/BackendTest.php
+++ b/search_api_db/tests/src/Kernel/BackendTest.php
@@ -1076,6 +1076,7 @@ class BackendTest extends KernelTestBase {
     );
     $field = Utility::createField($index, $property_name, $field_info);
     $index->addField($field);
+    $index->save();
   }
 
 }
diff --git a/src/Entity/Index.php b/src/Entity/Index.php
index 188ac80..9c55a45 100644
--- a/src/Entity/Index.php
+++ b/src/Entity/Index.php
@@ -117,6 +117,13 @@ class Index extends ConfigEntityBase implements IndexInterface {
   protected $field_settings = array();
 
   /**
+   * An array of field instances.
+   *
+   * @var \Drupal\search_api\Item\FieldInterface[]|null
+   */
+  protected $fieldInstances = NULL;
+
+  /**
    * An array of options configuring this index.
    *
    * @var array
@@ -605,7 +612,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       throw new SearchApiException(new FormattableMarkup('Cannot add field with machine name %field_id: machine name is already taken.', $args));
     }
 
-    $this->field_settings[$field_id] = $field->getSettings();
+    $this->fieldInstances[$field_id] = $field;
 
     return $this;
   }
@@ -624,11 +631,11 @@ class Index extends ConfigEntityBase implements IndexInterface {
     }
     if (isset($this->getFields()[$new_field_id])) {
       $args['%field_id'] = $new_field_id;
-      throw new SearchApiException(new FormattableMarkup('%field_id is a reserved value and cannot be used as the machine name of a normal field.', $args));
+      throw new SearchApiException(new FormattableMarkup('%field_id already exists and can\'t be used as a new field id.', $args));
     }
 
-    $this->field_settings[$new_field_id] = $this->field_settings[$old_field_id];
-    unset($this->field_settings[$old_field_id]);
+    $this->fieldInstances[$new_field_id] = $this->fieldInstances[$old_field_id];
+    unset($this->fieldInstances[$old_field_id]);
 
     return $this;
   }
@@ -646,7 +653,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
       throw new SearchApiException(new FormattableMarkup('Cannot remove field with machine name %field_id: field is locked.', $args));
     }
 
-    unset($this->field_settings[$field_id]);
+    unset($this->fieldInstances[$field_id]);
 
     return $this;
   }
@@ -655,11 +662,17 @@ class Index extends ConfigEntityBase implements IndexInterface {
    * {@inheritdoc}
    */
   public function getFields() {
+    if ($this->fieldInstances !== NULL) {
+      return $this->fieldInstances;
+    }
+
     $fields = array();
     foreach ($this->field_settings as $key => $field_info) {
       $fields[$key] = Utility::createField($this, $key, $field_info);
     }
 
+    $this->fieldInstances = $fields;
+
     return $fields;
   }
 
@@ -689,8 +702,8 @@ class Index extends ConfigEntityBase implements IndexInterface {
    */
   public function getFulltextFields() {
     $fulltext_fields = array();
-    foreach ($this->field_settings as $key => $field_info) {
-      if (Utility::isTextType($field_info['type'])) {
+    foreach ($this->getFields() as $key => $field) {
+      if (Utility::isTextType($field->getType())) {
         $fulltext_fields[] = $key;
       }
     }
@@ -996,6 +1009,11 @@ class Index extends ConfigEntityBase implements IndexInterface {
       $this->disable();
     }
 
+    $this->field_settings = array();
+    foreach ($this->getFields() as $field_id => $field) {
+      $this->field_settings[$field_id] = $field->getSettings();
+    }
+
     // Remove all "locked" and "hidden" flags from all fields of the index. If
     // they are still valid, they should be re-added by the processors.
     foreach ($this->field_settings as $field_id => $field_settings) {
@@ -1558,6 +1576,7 @@ class Index extends ConfigEntityBase implements IndexInterface {
     unset($properties['trackerInstance']);
     unset($properties['serverInstance']);
     unset($properties['processorInstances']);
+    unset($properties['fieldInstances']);
     unset($properties['cache']);
     return array_keys($properties);
   }
diff --git a/tests/src/Kernel/CliTest.php b/tests/src/Kernel/CliTest.php
index 95c3395..c99833e 100644
--- a/tests/src/Kernel/CliTest.php
+++ b/tests/src/Kernel/CliTest.php
@@ -109,8 +109,8 @@ class CliTest extends KernelTestBase {
     $total_items = $index->getTrackerInstance()->getTotalItemsCount();
     $indexed_items = $index->getTrackerInstance()->getIndexedItemsCount();
 
-    $this->assertEquals($total_items, 2, 'The 2 items are tracked.');
-    $this->assertEquals($indexed_items, 0, 'No items are indexed');
+    $this->assertEquals(2, $total_items,'The 2 items are tracked.');
+    $this->assertEquals(0, $indexed_items, 'No items are indexed');
 
     EntityTest::create(array(
       'name' => 'foo bar baz föö smile',
@@ -130,8 +130,8 @@ class CliTest extends KernelTestBase {
     $total_items = $index->getTrackerInstance()->getTotalItemsCount();
     $indexed_items = $index->getTrackerInstance()->getIndexedItemsCount();
 
-    $this->assertEquals($total_items, 4, 'All 4 items are tracked.');
-    $this->assertEquals($indexed_items, 2, '2 items are indexed');
+    $this->assertEquals(4, $total_items, 'All 4 items are tracked.');
+    $this->assertEquals(0, $indexed_items, '0 items are indexed');
   }
 
 }