diff --git a/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php b/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
index 08c9c2d437..eafe50b32d 100644
--- a/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
@@ -5,6 +5,7 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\TempStore\PrivateTempStoreFactory;
+use GuzzleHttp\ClientInterface;
 use GuzzleHttp\Exception\TransferException;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -23,16 +24,26 @@ class CredentialForm extends MigrateUpgradeFormBase {
   protected $renderer;
 
   /**
+   * The HTTP client to fetch the feed data with.
+   *
+   * @var \GuzzleHttp\ClientInterface
+   */
+  protected $httpClient;
+
+  /**
    * CredentialForm constructor.
    *
    * @param \Drupal\Core\Render\RendererInterface $renderer
    *   The renderer service.
    * @param \Drupal\Core\TempStore\PrivateTempStoreFactory $tempstore_private
    *   The private tempstore factory.
+   * @param \GuzzleHttp\ClientInterface $http_client
+   *   A Guzzle client object.
    */
-  public function __construct(RendererInterface $renderer, PrivateTempStoreFactory $tempstore_private) {
+  public function __construct(RendererInterface $renderer, PrivateTempStoreFactory $tempstore_private, ClientInterface $http_client) {
     parent::__construct($tempstore_private);
     $this->renderer = $renderer;
+    $this->httpClient = $http_client;
   }
 
   /**
@@ -41,7 +52,8 @@ public function __construct(RendererInterface $renderer, PrivateTempStoreFactory
   public static function create(ContainerInterface $container) {
     return new static(
       $container->get('renderer'),
-      $container->get('tempstore.private')
+      $container->get('tempstore.private'),
+      $container->get('http_client')
     );
   }
 
@@ -202,10 +214,10 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       $connection = $this->getConnection($database);
       $version = (string) $this->getLegacyDrupalVersion($connection);
       if (!$version) {
-        $errors[$driver . '][0'] = $this->t('Source database does not contain a recognizable Drupal version.');
+        $errors[$database['driver'] . '][database'] = $this->t('Source database does not contain a recognizable Drupal version.');
       }
       elseif ($version !== (string) $form_state->getValue('version')) {
-        $errors[$driver . '][0'] = $this->t('Source database is Drupal version @version but version @selected was selected.',
+        $errors['version'] = $this->t('Source database is Drupal version @version but version @selected was selected.',
           [
             '@version' => $version,
             '@selected' => $form_state->getValue('version'),
@@ -217,7 +229,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       }
     }
     catch (\Exception $e) {
-      $errors[$driver . '][0'] = $e->getMessage();
+      $errors[$driver] = $e->getMessage();
     }
 
     // Check that sources files are available.
@@ -241,7 +253,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
         }
         else {
           try {
-            \Drupal::httpClient()->head($source);
+            $this->httpClient->head($source);
           }
           catch (TransferException $e) {
             $errors[$key] = $msg . ' ' . $e->getMessage();
@@ -265,20 +277,17 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
   protected function buildErrorList(array $errors, FormStateInterface $form_state) {
     $items = [];
     foreach ($errors as $name => $message) {
-      $form_state->setErrorByName($name . '][0');
+      $form_state->setErrorByName($name);
       $items[] = $message;
     }
-    $msg_singular = $this->t('Resolve the issue below to continue the upgrade.');
-    $msg_plural = $this->t('Resolve the issues below to continue the upgrade.');
-    $msg = $this->formatPlural(count($errors), $msg_singular, $msg_plural);
 
     $list = [
-      '#title' => $msg,
+      '#title' => $this->t('Resolve all issues below to continue the upgrade.'),
       '#theme' => 'item_list',
       '#items' => $items,
     ];
     $name = current(array_keys($errors));
-    $form_state->setErrorByName($name, $this->renderer->renderPlain($list));
+    $form_state->setErrorByName($name . '][0', $this->renderer->renderPlain($list));
   }
 
   /**