diff --git a/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
index 03b26c5dc2..09a7fc6145 100644
--- a/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
+++ b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
@@ -115,7 +115,10 @@ public static function run($initial_ids, $config, &$context) {
     if ($definition['destination']['plugin'] === 'entity:file') {
       // Make sure we have a single trailing slash.
       $configuration['source']['constants']['source_base_path'] = rtrim($config['source_base_path'], '/') . '/';
-      if ($definition['source']['scheme'] === 'private') {
+      // Use the private file path if the scheme property is set in the source
+      // plugin definition and is 'private'.
+      $scheme = $definition['source']['scheme'] ?? NULL;
+      if ($scheme === 'private') {
         $configuration['source']['constants']['source_base_path'] = rtrim($config['source_private_file_path'], '/') . '/';
       }
     }