diff --git a/src/Tests/CaptchaBaseWebTestCase.php b/src/Tests/CaptchaBaseWebTestCase.php
index 538ef87..4c81aff 100755
--- a/src/Tests/CaptchaBaseWebTestCase.php
+++ b/src/Tests/CaptchaBaseWebTestCase.php
@@ -229,10 +229,10 @@ abstract class CaptchaBaseWebTestCase extends WebTestBase {
   protected function getMathCaptchaSolutionFromForm($form_html_id = NULL) {
     // Get the math challenge.
     if (!$form_html_id) {
-      $elements = $this->xpath('//div[@class="form-item form-type-textfield form-item-captcha-response"]/span[@class="field-prefix"]');
+      $elements = $this->xpath('//div[contains(@class, "form-item-captcha-response")]/span[@class="field-prefix"]');
     }
     else {
-      $elements = $this->xpath('//form[@id="' . $form_html_id . '"]//div[@class="form-item form-type-textfield form-item-captcha-response"]/span[@class="field-prefix"]');
+      $elements = $this->xpath('//form[@id="' . $form_html_id . '"]//div[contains(@class, "form-item-captcha-response")]/span[@class="field-prefix"]');
     }
     $this->assert('pass', json_encode($elements));
     $challenge = (string) $elements[0];
diff --git a/src/Tests/CaptchaTestCase.php b/src/Tests/CaptchaTestCase.php
index 12e0cef..7681406 100755
--- a/src/Tests/CaptchaTestCase.php
+++ b/src/Tests/CaptchaTestCase.php
@@ -7,6 +7,10 @@
 
 namespace Drupal\captcha\Tests;
 
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+
 /**
  * Tests CAPTCHA main test case sensitivity.
  *
@@ -209,4 +213,48 @@ class CaptchaTestCase extends CaptchaBaseWebTestCase {
     $this->assertCaptchaPresence(TRUE);
   }
 
+  /**
+   * Tests that the CAPTCHA is not changed on AJAX form rebuilds.
+   */
+  public function testAjaxFormRebuild() {
+    // Setup captcha point for user edit form.
+    \Drupal::entityManager()->getStorage('captcha_point')->create([
+      'id' => 'user_form',
+      'formId' => 'user_form',
+      'status' => TRUE,
+      'captchaType' => 'captcha/Math',
+    ])->save();
+
+    // Add multiple text field on user edit form.
+    $field_storage_config = FieldStorageConfig::create([
+      'field_name' => 'field_texts',
+      'type' => 'string',
+      'entity_type' => 'user',
+      'cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED,
+    ]);
+    $field_storage_config->save();
+    FieldConfig::create([
+      'field_storage' => $field_storage_config,
+      'bundle' => 'user',
+    ])->save();
+    entity_get_form_display('user', 'user', 'default')->setComponent('field_texts', [
+      'type' => 'string_textfield',
+      'weight' => 10,
+    ])->save();
+
+    // Create and login a user.
+    $user = $this->drupalCreateUser([]);
+    $this->drupalLogin($user);
+
+    // On edit form, add another item and save.
+    $this->drupalGet("user/{$user->id()}/edit");
+    $this->drupalPostAjaxForm(NULL, [], 'field_texts_add_more');
+    $this->drupalPostForm(NULL, [
+      'captcha_response' => $this->getMathCaptchaSolutionFromForm('user-form'),
+    ], t('Save'));
+
+    // No error.
+    $this->assertText(t('The changes have been saved.'));
+  }
+
 }