diff --git a/core/modules/migrate_drupal/src/MigrationConfigurationTrait.php b/core/modules/migrate_drupal/src/MigrationConfigurationTrait.php
index 0aca5be..18cc5ca 100644
--- a/core/modules/migrate_drupal/src/MigrationConfigurationTrait.php
+++ b/core/modules/migrate_drupal/src/MigrationConfigurationTrait.php
@@ -56,7 +56,7 @@ protected function getSystemData(Connection $connection) {
         $system_data[$result['type']][$result['name']] = $result;
       }
     }
-    catch (\Exception $e) {
+    catch (\PDOException $e) {
       // The table might not exist for example in tests.
     }
     return $system_data;
@@ -183,10 +183,18 @@ protected function getLegacyDrupalVersion(Connection $connection) {
     // For Drupal 8 (and we're predicting beyond) the schema version is in the
     // key_value store.
     elseif ($connection->schema()->tableExists('key_value')) {
-      $result = $connection
-        ->query("SELECT value FROM {key_value} WHERE collection = :system_schema  and name = :module", [':system_schema' => 'system.schema', ':module' => 'system'])
-        ->fetchField();
-      $version_string = unserialize($result);
+      try {
+        $result = $connection
+          ->query("SELECT value FROM {key_value} WHERE collection = :system_schema  and name = :module", [
+            ':system_schema' => 'system.schema',
+            ':module' => 'system'
+          ])
+          ->fetchField();
+        $version_string = unserialize($result);
+      }
+      catch (\PDOException $e) {
+        $version_string = FALSE;
+      }
     }
     else {
       $version_string = FALSE;
diff --git a/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php b/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
index deeebe5..a09c35c 100644
--- a/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
@@ -3,9 +3,12 @@
 namespace Drupal\migrate_drupal_ui\Form;
 
 use Drupal\Component\Utility\UrlHelper;
+use Drupal\Core\Database\DatabaseException;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\TempStore\PrivateTempStoreFactory;
+use Drupal\migrate\Exception\RequirementsException;
+use Drupal\migrate\Plugin\Exception\BadPluginDefinitionException;
 use GuzzleHttp\ClientInterface;
 use GuzzleHttp\Exception\TransferException;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -226,26 +229,45 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       }
     }
     else {
+      $error_message = [
+        '#title' => $this->t('Resolve the issue below to continue the upgrade.'),
+        '#theme' => 'item_list',
+      ];
+      // Validate the database connection.
       try {
         $connection = $this->getConnection($database);
         $version = (string) $this->getLegacyDrupalVersion($connection);
-        if (!$version) {
-          $this->errors[$database['driver'] . '][database'] = $this->t('Source database does not contain a recognizable Drupal version.');
-        }
-        elseif ($version !== (string) $form_state->getValue('version')) {
-          $this->errors['version'] = $this->t('Source database is Drupal version @version but version @selected was selected.',
-            [
+      }
+      catch (DatabaseException $e) {
+        $error_message['#items'] = [$e->getMessage()];
+        $this->errors[$database['driver'] . '][database'] = $this->renderer->renderPlain($error_message);
+      }
+      // Validate the Drupal version.
+      if (!isset($version)) {
+        $error_message['#items'] = [$this->t('Source database does not contain a recognizable Drupal version.')];
+        $this->errors[$database['driver'] . '][database'] = $this->renderer->renderPlain($error_message);
+      }
+      else {
+        if ($version !== (string) $form_state->getValue('version')) {
+          $message = $this->t('Source database is Drupal version @version but version @selected was selected.', [
               '@version' => $version,
               '@selected' => $form_state->getValue('version'),
-            ]);
-        }
-        else {
-          // Setup migrations and save form data to private store.
-          $this->setupMigrations($database, $form_state);
+          ]);
+          $error_message['#items'] = [$message];
+          $this->errors['version'] = $this->renderer->renderPlain($error_message);
         }
       }
-      catch (\Exception $e) {
-        $this->errors[$database['driver'] . '][database'] = $e->getMessage();
+      // Setup migrations and save form data to private store.
+      try {
+        $this->setupMigrations($database, $form_state);
+      }
+      catch (BadPluginDefinitionException $e) {
+        $error_message['#items'] = [$e->getMessage()];
+        $this->errors[$database['driver'] . '][database'] = $this->renderer->renderPlain($error_message);
+      }
+      catch (RequirementsException $e) {
+        $error_message['#items'] = [$e->getMessage()];
+        $this->errors[$database['driver'] . '][database'] = $this->renderer->renderPlain($error_message);
       }
     }
 
diff --git a/core/modules/migrate_drupal_ui/src/Form/IncrementalForm.php b/core/modules/migrate_drupal_ui/src/Form/IncrementalForm.php
index 8090190..617514f 100644
--- a/core/modules/migrate_drupal_ui/src/Form/IncrementalForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/IncrementalForm.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\migrate_drupal_ui\Form;
 
-use Drupal\Core\Database\DatabaseExceptionWrapper;
 use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\State\StateInterface;
@@ -92,29 +91,6 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validateForm(array &$form, FormStateInterface $form_state) {
-    // Retrieve the database driver from state.
-    $database_state_key = $this->state->get('migrate.fallback_state_key', '');
-    if ($database_state_key) {
-      try {
-        $database = $this->state->get($database_state_key, [])['database'];
-        if ($connection = $this->getConnection($database)) {
-          if ($version = $this->getLegacyDrupalVersion($connection)) {
-            $this->setupMigrations($database, $form_state);
-            $valid_legacy_database = TRUE;
-          }
-        }
-      }
-      catch (DatabaseExceptionWrapper $exception) {
-        // Hide DB exceptions and forward to the DB credentials form. In that
-        // form we can more properly display errors and accept new credentials.
-      }
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     $this->store->set('step', 'credential');
     $form_state->setRedirect('migrate_drupal_ui.upgrade_credential');