diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 369fdfc..9013e7d 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2438,6 +2438,8 @@ function drupal_fast_404() {
  * Returns TRUE if a Drupal installation is currently being attempted.
  */
 function drupal_installation_attempted() {
+  return isset($GLOBALS['install_state']);
+  // @todo Entirely incompatible with non-interactive installer invoked from SimpleTest.
   return defined('MAINTENANCE_MODE') && MAINTENANCE_MODE == 'install';
 }
 
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 37b3281..3a3937c 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -251,14 +251,6 @@ function install_begin_request(&$install_state) {
     drupal_override_server_variables($install_state['server']);
   }
 
-  // The user agent header is used to pass a database prefix in the request when
-  // running tests. However, for security reasons, it is imperative that no
-  // installation be permitted using such a prefix.
-  if (isset($_SERVER['HTTP_USER_AGENT']) && strpos($_SERVER['HTTP_USER_AGENT'], "simpletest") !== FALSE) {
-    header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
-    exit;
-  }
-
   drupal_bootstrap(DRUPAL_BOOTSTRAP_CONFIGURATION);
 
   // This must go after drupal_bootstrap(), which unsets globals!
@@ -1296,7 +1288,7 @@ function install_select_language(&$install_state) {
       }
       // One language, but not an interactive installation. Assume the user
       // knows what he is doing.
-      $langcode = current($files);
+      $file = current($files);
       $install_state['parameters']['langcode'] = $file->langcode;
       return;
     }
diff --git a/core/includes/install.inc b/core/includes/install.inc
index 72adf1c..4a2d2df 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -94,10 +94,10 @@ function drupal_load_updates() {
  * @see install_profile_info()
  */
 function drupal_install_profile_distribution_name() {
+  global $install_state;
   // During installation, the profile information is stored in the global
   // installation state (it might not be saved anywhere yet).
-  if (drupal_installation_attempted()) {
-    global $install_state;
+  if (isset($install_state['profile_info']['distribution_name'])) {
     return $install_state['profile_info']['distribution_name'];
   }
   // At all other times, we load the profile via standard methods.
diff --git a/core/modules/simpletest/drupal_web_test_case.php b/core/modules/simpletest/drupal_web_test_case.php
index 5d868a2..10f4431 100644
--- a/core/modules/simpletest/drupal_web_test_case.php
+++ b/core/modules/simpletest/drupal_web_test_case.php
@@ -1319,16 +1319,9 @@ class DrupalWebTestCase extends DrupalTestCase {
     $this->originalProfile = drupal_get_profile();
     $clean_url_original = variable_get('clean_url', 0);
 
-    // Set to English to prevent exceptions from utf8_truncate() from t()
-    // during install if the current language is not 'en'.
-    // The following array/object conversion is copied from language_default().
-    $language = (object) array(
-      'langcode' => 'en',
-      'name' => 'English',
-      'direction' => 0,
-      'enabled' => 1,
-      'weight' => 0,
-    );
+    // Backup current user.
+    $this->originalUser = $user;
+    drupal_save_session(FALSE);
 
     // Save and clean shutdown callbacks array because it static cached and
     // will be changed by the test run. If we don't, then it will contain
@@ -1373,12 +1366,52 @@ class DrupalWebTestCase extends DrupalTestCase {
     // the test's profile as a module. Without this, the installation profile of
     // the parent site (executing the test) is registered, and the test
     // profile's hook_install() and other hook implementations are never invoked.
-    $conf['install_profile'] = $this->profile;
-
-    include_once DRUPAL_ROOT . '/core/includes/install.inc';
-    drupal_install_system();
-
-    $this->preloadRegistry();
+    // @todo Double-check this.
+//    $conf['install_profile'] = $this->profile;
+
+    // Run the Drupal installer non-interactively.
+    // @see install.php, install.core.inc
+    require_once DRUPAL_ROOT . '/core/includes/install.core.inc';
+    $this->root_user = (object) array(
+      'name' => 'admin',
+      'mail' => 'admin@example.com',
+      'pass_raw' => $this->randomName(),
+    );
+    $settings = array(
+      'parameters' => array(
+        'profile' => $this->profile,
+        'langcode' => 'en',
+      ),
+      'forms' => array(
+        'install_settings_form' => array(
+          'driver' => $connection_info['default']['driver'],
+          'username' => $connection_info['default']['username'],
+          'host' => $connection_info['default']['host'],
+          'port' => $connection_info['default']['port'],
+          'password' => $connection_info['default']['password'],
+          'database' => $connection_info['default']['database'],
+          'prefix' => $connection_info['default']['prefix'],
+        ),
+        'install_configure_form' => array(
+          'site_name' => 'Drupal',
+          'site_mail' => 'simpletest@example.com',
+          'account' => array(
+            'name' => $this->root_user->name,
+            'mail' => $this->root_user->mail,
+            'pass' => array(
+              'pass1' => $this->root_user->pass_raw,
+              'pass2' => $this->root_user->pass_raw,
+            ),
+          ),
+          'update_status_module' => array(
+            1 => FALSE,
+            2 => FALSE,
+          ),
+          'clean_url' => $clean_url_original,
+        ),
+      ),
+    );
+    install_drupal($settings);
 
     // Set path variables.
     variable_set('file_public_path', $public_files_directory);
@@ -1411,31 +1444,15 @@ class DrupalWebTestCase extends DrupalTestCase {
       $this->assertTrue($success, t('Enabled modules: %modules', array('%modules' => implode(', ', $modules))));
     }
 
-    // Run the profile tasks.
-    $install_profile_module_exists = db_query("SELECT 1 FROM {system} WHERE type = 'module' AND name = :name", array(
-      ':name' => $this->profile,
-    ))->fetchField();
-    if ($install_profile_module_exists) {
-      module_enable(array($this->profile), FALSE);
-    }
-
     // Reset/rebuild all data structures after enabling the modules.
     $this->resetAll();
 
-    // Run cron once in that environment, as install.php does at the end of
-    // the installation process.
-    drupal_cron_run();
-
     // Log in with a clean $user.
-    $this->originalUser = $user;
-    drupal_save_session(FALSE);
     $user = user_load(1);
 
     // Restore necessary variables.
-    variable_set('install_task', 'done');
-    variable_set('clean_url', $clean_url_original);
-    variable_set('site_mail', 'simpletest@example.com');
     variable_set('date_default_timezone', date_default_timezone_get());
+
     // Set up English language.
     unset($GLOBALS['conf']['language_default']);
     $language_interface = language_default();