diff --git a/core/lib/Drupal/Core/Extension/Extension.php b/core/lib/Drupal/Core/Extension/Extension.php
index 3c765fe..e1e9b3d 100644
--- a/core/lib/Drupal/Core/Extension/Extension.php
+++ b/core/lib/Drupal/Core/Extension/Extension.php
@@ -166,8 +166,9 @@ public function __call($method, array $args) {
    * Serializes the Extension object in the most optimized way.
    */
   public function serialize() {
+    // Don't serialize the app root, since this could change if the install is
+    // moved..
     $data = array(
-      'root' => $this->root,
       'type' => $this->type,
       'pathname' => $this->pathname,
       'filename' => $this->filename,
@@ -188,7 +189,8 @@ public function serialize() {
    */
   public function unserialize($data) {
     $data = unserialize($data);
-    $this->root = $data['root'];
+    // Get the app root from the container.
+    $this->root = DRUPAL_ROOT;
     $this->type = $data['type'];
     $this->pathname = $data['pathname'];
     $this->filename = $data['filename'];
diff --git a/core/modules/system/src/Controller/DbUpdateController.php b/core/modules/system/src/Controller/DbUpdateController.php
index 28ab72b..cde11f7 100644
--- a/core/modules/system/src/Controller/DbUpdateController.php
+++ b/core/modules/system/src/Controller/DbUpdateController.php
@@ -210,9 +210,7 @@ protected function info(Request $request) {
     );
 
     $info[] = $this->t("<strong>Back up your code</strong>. Hint: when backing up module code, do not leave that backup in the 'modules' or 'sites/*/modules' directories as this may confuse Drupal's auto-discovery mechanism.");
-    $info[] = $this->t('Put your site into <a href="@url">maintenance mode</a>.', array(
-      '@url' => Url::fromRoute('system.site_maintenance_mode')->toString(TRUE)->getGeneratedUrl(),
-    ));
+    $info[] = $this->t('Put your site into maintenance mode.');
     $info[] = $this->t('<strong>Back up your database</strong>. This process will change your database values and in case of emergency you may need to revert to a backup.');
     $info[] = $this->t('Install your new files in the appropriate location, as described in the handbook.');
     $build['info'] = array(
@@ -228,7 +226,7 @@ protected function info(Request $request) {
       '#type' => 'link',
       '#title' => $this->t('Continue'),
       '#attributes' => array('class' => array('button', 'button--primary')),
-      '#url' => Url::fromUri($request->getUriForPath('/selection')),
+      '#url' => Url::fromUri('base://selection'),
     );
     return $build;
   }
@@ -484,7 +482,7 @@ protected function results(Request $request) {
    */
   public function requirements($severity, array $requirements, Request $request) {
     $options = $severity == REQUIREMENT_WARNING ? array('continue' => 1) : array();
-    $try_again_url = Url::fromUri($request->getUriForPath(''))->setOptions(['query' => $options])->toString(TRUE)->getGeneratedUrl();
+    $try_again_url = Url::fromUri('base://')->setOptions(['query' => $options])->toString(TRUE)->getGeneratedUrl();
 
     $build['status_report'] = array(
       '#theme' => 'status_report',
@@ -580,7 +578,7 @@ protected function triggerBatch(Request $request) {
     );
     batch_set($batch);
 
-    return batch_process(Url::fromUri($request->getUriForPath('/results')), Url::fromUri($request->getUriForPath('/start')));
+    return batch_process(Url::fromUri('base://results'), Url::fromUri('base://start'));
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Update/UpdatePathTestBase.php b/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
index d3d103d..dd22488 100644
--- a/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
+++ b/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
@@ -173,9 +173,6 @@ protected function setUp() {
     // Add the config directories to settings.php.
     drupal_install_config_directories();
 
-    // Install any additional modules.
-    $this->installModulesFromClassProperty($container);
-
     // Restore the original Simpletest batch.
     $this->restoreBatch();
 
@@ -183,6 +180,7 @@ protected function setUp() {
     $this->rebuildAll();
 
     // Replace User 1 with the user created here.
+    // @todo: do this without saving the user account.
     /** @var \Drupal\user\UserInterface $account */
     $account = User::load(1);
     $account->setPassword($this->rootUser->pass_raw);
@@ -260,7 +258,9 @@ protected function rebuildAll() {
     // We know the rebuild causes notices, so don't exit on failure.
     $die_on_fail = $this->dieOnFail;
     $this->dieOnFail = FALSE;
-    parent::rebuildAll();
+
+    // Initialize the container. parent::rebuildall() is not safe to call here.
+    $this->container = \Drupal::getContainer();
 
     // Remove the notices we get due to the menu link rebuild prior to running
     // the system updates for the schema change.