diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 6c69150..04dd0a4 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -889,14 +889,13 @@ function drupal_get_filename($type, $name, $filename = NULL) {
 
   // Profiles are a special case: they have a fixed location and naming.
   if ($type == 'profile') {
-    $profile_filename = "profiles/$name/$name.profile";
-    $files[$type][$name] = file_exists($profile_filename) ? $profile_filename : FALSE;
+    $files[$type][$name] = "profiles/$name/$name.profile";
   }
   if (!isset($files[$type])) {
     $files[$type] = array();
   }
 
-  if (!empty($filename) && file_exists($filename)) {
+  if (!empty($filename)) {
     $files[$type][$name] = $filename;
   }
   elseif (isset($files[$type][$name])) {
@@ -909,10 +908,7 @@ function drupal_get_filename($type, $name, $filename = NULL) {
   else {
     try {
       if (function_exists('db_query')) {
-        $file = db_query("SELECT filename FROM {system} WHERE name = :name AND type = :type", array(':name' => $name, ':type' => $type))->fetchField();
-        if (file_exists(DRUPAL_ROOT . '/' . $file)) {
-          $files[$type][$name] = $file;
-        }
+        $files[$type][$name] = db_query("SELECT filename FROM {system} WHERE name = :name AND type = :type", array(':name' => $name, ':type' => $type))->fetchField();
       }
     }
     catch (Exception $e) {
diff --git a/core/includes/update.inc b/core/includes/update.inc
index 1de14f0..b2287d9 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -91,6 +91,13 @@ function update_prepare_d8_bootstrap() {
   // drupal_get_installed_schema_version().
   $system_schema = drupal_get_installed_schema_version('system');
   if ($system_schema < 8000) {
+
+    // We need to rescan the modules so their actual place on the file system
+    // is updated. see http://drupal.org/node/752730.
+    include_once DRUPAL_ROOT . '/core/includes/module.inc';
+    include_once DRUPAL_ROOT . '/core/modules/system/system.module';
+    system_rebuild_module_data();
+
     $has_required_schema = $system_schema >= REQUIRED_D7_SCHEMA_VERSION;
     $requirements = array(
       'drupal 7 version' => array(
@@ -184,7 +191,8 @@ function update_module_add_to_system($modules = array()) {
   );
   foreach ($modules as $module) {
     $module_info = drupal_parse_info_file('core/modules/' . $module . '/' . $module . '.info');
-    db_insert('system')
+    db_merge('system')
+      ->key(array('name'), array($module))
       ->fields(array(
         'filename' => 'core/modules/' . $module . '/' . $module . '.module',
         'name' => $module,
diff --git a/core/update.php b/core/update.php
index dd338a2..47ba960 100644
--- a/core/update.php
+++ b/core/update.php
@@ -283,10 +283,10 @@ function update_access_allowed() {
   if (!empty($update_free_access)) {
     return TRUE;
   }
-  // Calls to user_access() might fail during the Drupal 6 to 7 update process,
+  // Calls to user_access() might fail during the Drupal 7 to 8 update process,
   // so we fall back on requiring that the user be logged in as user #1.
   try {
-    require_once DRUPAL_ROOT . '/' . drupal_get_path('module', 'user') . '/user.module';
+    require_once DRUPAL_ROOT . '/core/modules/user/user.module';
     return user_access('administer software updates');
   }
   catch (Exception $e) {