diff --git a/core/includes/common.inc b/core/includes/common.inc
index b68d6d0..0336161 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -3643,7 +3643,13 @@ function drupal_prepare_page($page) {
   }
 
   // Modules can add elements to $page as needed in hook_page_build().
-  foreach (\Drupal::moduleHandler()->getImplementations('page_build') as $module) {
+  if (!defined('MAINTENANCE_MODE')) {
+    $implementations = \Drupal::moduleHandler()->getImplementations('page_build');
+  }
+  else {
+    $implementations = array('system');
+  }
+  foreach ($implementations as $module) {
     $function = $module . '_page_build';
     $function($page);
   }
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 50d78f4..7f494c5 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -409,15 +409,12 @@ function install_begin_request(&$install_state) {
 
   // Override the module list with a minimal set of modules.
   $module_handler = \Drupal::moduleHandler();
-  $original_module_list = $module_handler->getModuleList();
-  $module_list = array();
-  $module_list['system'] = 'core/modules/system/system.module';
-  system_register('module', 'system', $module_list['system']);
-  if (isset($original_module_list['user'])) {
-    $module_list['user'] = 'core/modules/user/user.module';
-    system_register('module', 'user', $module_list['user']);
-  }
-  if ($profile) {
+  $module_list = $module_handler->getModuleList();
+  if (!$module_handler->moduleExists('system')) {
+    $module_list['system'] = 'core/modules/system/system.module';
+    system_register('module', 'system', $module_list['system']);
+  }
+  if ($profile && !$module_handler->moduleExists($profile)) {
     $module_list[$profile] = $install_state['profiles'][$profile]->uri;
     system_register('profile', $profile, $module_list[$profile]);
   }