diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 1616f18..a016540 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -20,6 +20,7 @@
 use Drupal\Core\Site\Settings;
 use Drupal\Core\StringTranslation\Translator\FileTranslation;
 use Drupal\Core\StackMiddleware\ReverseProxyMiddleware;
+use Drupal\Core\StreamWrapper\PublicStream;
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Url;
@@ -1036,6 +1037,21 @@ function install_base_system(&$install_state) {
   // Install system.module.
   drupal_install_system($install_state);
 
+  // Prevent the installer from using the system temporary directory after the
+  // system module has been installed.
+  if (drupal_valid_test_ua()) {
+    // While the temporary directory could be preset/enforced in settings.php
+    // like the public files directory, some tests expect it to be configurable
+    // in the UI. If declared in settings.php, they would no longer be
+    // configurable. The temporary directory needs to match what is set in each
+    // test types ::prepareEnvironment() step.
+    $temporary_directory = dirname(PublicStream::basePath()) . '/temp';
+    file_prepare_directory($temporary_directory, FILE_MODIFY_PERMISSIONS | FILE_CREATE_DIRECTORY);
+    \Drupal::configFactory()->getEditable('system.file')
+      ->set('path.temporary', $temporary_directory)
+      ->save();
+  }
+
   // Call file_ensure_htaccess() to ensure that all of Drupal's standard
   // directories (e.g., the public files directory and config directory) have
   // appropriate .htaccess files. These directories will have already been
diff --git a/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php b/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
index dbbd962..96bcdc8 100644
--- a/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
+++ b/core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
@@ -316,15 +316,8 @@ protected function initSettings() {
   protected function initConfig(ContainerInterface $container) {
     $config = $container->get('config.factory');
 
-    // Manually create and configure private and temporary files directories.
-    // While these could be preset/enforced in settings.php like the public
-    // files directory above, some tests expect them to be configurable in the
-    // UI. If declared in settings.php, they would no longer be configurable.
+    // Manually create the private directory.
     file_prepare_directory($this->privateFilesDirectory, FILE_CREATE_DIRECTORY);
-    file_prepare_directory($this->tempFilesDirectory, FILE_CREATE_DIRECTORY);
-    $config->getEditable('system.file')
-      ->set('path.temporary', $this->tempFilesDirectory)
-      ->save();
 
     // Manually configure the test mail collector implementation to prevent
     // tests from sending out emails and collect them in state instead.
diff --git a/core/lib/Drupal/Core/Test/TestSetupTrait.php b/core/lib/Drupal/Core/Test/TestSetupTrait.php
index 32e6fca..31849c8 100644
--- a/core/lib/Drupal/Core/Test/TestSetupTrait.php
+++ b/core/lib/Drupal/Core/Test/TestSetupTrait.php
@@ -92,8 +92,12 @@
   /**
    * The temporary file directory for the test environment.
    *
+   * This value has to match the temporary directory created in
+   * install_base_system() for test installs.
+   *
    * @see \Drupal\simpletest\TestBase::prepareEnvironment()
    * @see \Drupal\Tests\BrowserTestBase::prepareEnvironment()
+   * @see install_base_system()
    *
    * @var string
    */