diff --git a/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php b/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
index 8a75202b9b..583d94f0f3 100644
--- a/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
+++ b/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
@@ -6,7 +6,6 @@
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\Entity\FieldStorageConfig;
-use Drupal\Core\Entity\Entity\EntityFormDisplay;
 
 /**
  * Tests user registration forms with additional fields.
@@ -87,19 +86,17 @@ public function testRegistrationWithUserFields() {
     $this->page->fillField('edit-name', $name);
     $this->page->fillField('edit-mail', $name . '@example.com');
     $this->page->pressButton('edit-submit');
-    $this->webAssert->assertWaitOnAjaxRequest();
     $this->assertRegistrationFormCacheTagsWithUserFields();
     $this->webAssert->pageTextContains(t('@name field is required.', ['@name' => $field->label()]));
 
     // Invalid input.
     $this->page->fillField('edit-test-user-field-0-value', '-1');
     $this->page->pressButton('edit-submit');
-    $this->webAssert->assertWaitOnAjaxRequest();
     $this->assertRegistrationFormCacheTagsWithUserFields();
     $this->webAssert->pageTextContains($field->label() . ' does not accept the value -1.');
 
     // Submit with valid data.
-    $value = mt_rand(1, 255);
+    $value = (string) mt_rand(1, 255);
     $this->page->fillField('edit-test-user-field-0-value', $value);
     $this->page->pressButton('edit-submit');
     // Check user fields.
@@ -114,12 +111,14 @@ public function testRegistrationWithUserFields() {
     foreach (['js', 'nojs'] as $js) {
       $this->drupalGet('user/register');
       $this->assertRegistrationFormCacheTagsWithUserFields();
-
       // Add two inputs.
       if ($js == 'js') {
-        $field_test_user_add_more = $this->page->find('css', 'edit-test-user-field-add-more');
+        $field_test_user_add_more = $this->page->find('css', '#edit-test-user-field-add-more');
         $field_test_user_add_more->click();
+        $this->webAssert->waitForField('input[name="test_user_field[1][value]"]');
+
         $field_test_user_add_more->click();
+        $this->webAssert->waitForField('input[name="test_user_field[2][value]"]');
       }
       else {
         $this->page->pressButton('edit-test-user-field-add-more');
@@ -130,8 +129,8 @@ public function testRegistrationWithUserFields() {
       $this->page->fillField('edit-name', $name);
       $this->page->fillField('edit-mail', $name . '@example.com');
       $this->page->fillField('edit-test-user-field-0-value', $value);
-      $this->page->fillField('edit-test-user-field-1-value', $value + 1);
-      $this->page->fillField('edit-test-user-field-2-value', $value + 1);
+      $this->page->fillField('edit-test-user-field-1-value', $value . '1');
+      $this->page->fillField('edit-test-user-field-2-value', $value . '2');
       $this->page->pressButton('edit-submit');
 
       // Check user fields.
@@ -139,8 +138,8 @@ public function testRegistrationWithUserFields() {
         ->loadByProperties(['name' => $name, 'mail' => $name . '@example.com']);
       $new_user = reset($accounts);
       $this->assertEquals($value, $new_user->test_user_field[0]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
-      $this->assertEquals($value + 1, $new_user->test_user_field[1]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
-      $this->assertEquals($value + 2, $new_user->test_user_field[2]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
+      $this->assertEquals($value . '1', $new_user->test_user_field[1]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
+      $this->assertEquals($value . '2', $new_user->test_user_field[2]->value, t('@js : The field value was correctly saved.', ['@js' => $js]));
     }
   }