diff -u b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
--- b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
+++ b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
@@ -119,7 +119,9 @@
       // Use the private file path if the scheme property is set in the source
       // plugin definition and is 'private' otherwise use the public file path.
       $scheme = $definition['source']['scheme'] ?? NULL;
-      $base_path = ($scheme === 'private') ? $config['source_private_file_path'] : $config['source_base_path'];
+      $base_path = ($scheme === 'private' && $config['source_private_file_path'])
+        ? $config['source_private_file_path']
+        : $config['source_base_path'];
       $configuration['source']['constants']['source_base_path'] = rtrim($base_path, '/') . '/';
     }
 
diff -u b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
--- b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
@@ -301,10 +301,7 @@
   }
 
   /**
-   * Provides the source base path for private files for the credential form.
-   *
-   * @return string|null
-   *   The source base path.
+   * {@inheritdoc}
    */
   protected function getSourcePrivateBasePath() {
     return NULL;
reverted:
--- b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/Upgrade7Test.php
+++ a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/Upgrade7Test.php
@@ -67,13 +67,6 @@
     return __DIR__ . '/files';
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  protected function getSourcePrivateBasePath() {
-    return __DIR__ . '/files';
-  }
-
   /**
    * {@inheritdoc}
    */
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/CredentialForm.php
@@ -193,7 +193,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#type' => 'textfield',
       '#title' => $this->t('Private files directory'),
       '#default_value' => '',
-      '#description' => $this->t('To import private files from your current Drupal site, enter a local file directory containing your site (e.g. /var/www/docroot).'),
+      '#description' => $this->t('To import private files from your current Drupal site, enter a local file directory containing your site (e.g. /var/www/docroot). Leave blank to use the same value as Public files directory.'),
       '#states' => [
         'visible' => [
           ':input[name="version"]' => ['value' => '7'],