diff --git a/core/lib/Drupal/Core/Extension/Extension.php b/core/lib/Drupal/Core/Extension/Extension.php
index 3c765fe..60392e5 100644
--- a/core/lib/Drupal/Core/Extension/Extension.php
+++ b/core/lib/Drupal/Core/Extension/Extension.php
@@ -137,13 +137,19 @@ public function getExtensionFilename() {
   /**
    * Loads the main extension file, if any.
    *
+   * Drupal will not attempt to load the file if it is not found.
+   *
    * @return bool
    *   TRUE if this extension has a main extension file, FALSE otherwise.
    */
   public function load() {
     if ($this->filename) {
-      include_once $this->root . '/' . $this->getPath() . '/' . $this->filename;
-      return TRUE;
+
+      $filepath = $this->root . '/' . $this->getPath() . '/' . $this->filename;
+      if (realpath($filepath)) {
+        include_once $this->root . '/' . $this->getPath() . '/' . $this->filename;
+        return TRUE;
+      }
     }
     return FALSE;
   }
@@ -188,7 +194,10 @@ public function serialize() {
    */
   public function unserialize($data) {
     $data = unserialize($data);
-    $this->root = $data['root'];
+    // If the root path does not exist, make an assumption that the extension
+    // root is in the current application root path. A database dump could have
+    // system-specific strings.
+    $this->root = realpath($data['root']) ? DRUPAL_ROOT : $data['root'];
     $this->type = $data['type'];
     $this->pathname = $data['pathname'];
     $this->filename = $data['filename'];
diff --git a/core/modules/system/src/Tests/Update/UpdatePathTestBase.php b/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
index 6c9b23b..1d052c3 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);
@@ -257,7 +255,9 @@ 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();
+
+    // Load the container without refreshing cache.
+    $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.