diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index 16076d7660feeb175f2899b98df2fa265a8be4b5..b6c90169506664e23247f8e568b099254f251d77 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -603,7 +603,11 @@ protected function setUp() {
 
     // Generate temporary prefixed database to ensure that tests have a clean starting point.
     $this->databasePrefix = Database::getConnection()->prefixTables('{simpletest' . mt_rand(1000, 1000000) . '}');
-    $conf['file_public_path'] = $this->originalFileDirectory . '/' . $this->databasePrefix;
+
+    // Create test directory.
+    $public_files_directory = $this->originalFileDirectory . '/simpletest/' . substr($this->databasePrefix, 10);
+    file_prepare_directory($public_files_directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS);
+    $conf['file_public_path'] = $public_files_directory;
 
     // Clone the current connection and replace the current prefix.
     $connection_info = Database::getConnectionInfo('default');