diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 0b1f633..1d8a746 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -10,6 +10,7 @@
 use Drupal\Component\Utility\Html;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\Unicode;
+use Drupal\Core\Database\Database;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\Logger\RfcLogLevel;
@@ -758,6 +759,22 @@ function drupal_installation_attempted() {
 }
 
 /**
+ * Check whether Drupal is installed.
+ *
+ * @return bool
+ *   TRUE if Drupal is installed, FALSE otherwise.
+ */
+function drupal_is_installed() {
+  // Check that a default database connection has been defined.
+  if (!Database::getConnectionInfo()) {
+    return FALSE;
+  }
+
+  // Check whether the sessions table exists.
+  return Database::getConnection()->schema()->tableExists('sessions');
+}
+
+/**
  * Gets the name of the currently active installation profile.
  *
  * When this function is called during Drupal's initial installation process,
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 890f7be..86130ba 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1096,14 +1096,8 @@ function install_verify_database_settings($site_path) {
  * Verify that the database is ready (no existing Drupal installation).
  */
 function install_verify_database_ready() {
-  $system_schema = system_schema();
-  end($system_schema);
-  $table = key($system_schema);
-
-  if ($database = Database::getConnectionInfo()) {
-    if (Database::getConnection()->schema()->tableExists($table)) {
-      throw new AlreadyInstalledException(\Drupal::service('string_translation'));
-    }
+  if (drupal_is_installed()) {
+    throw new AlreadyInstalledException(\Drupal::service('string_translation'));
   }
 }
 
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 2ddc3ee..7cfe0fb 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -13,7 +13,6 @@
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Config\BootstrapConfigStorageFactory;
 use Drupal\Core\Config\NullStorage;
-use Drupal\Core\Database\Database;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DependencyInjection\ServiceModifierInterface;
 use Drupal\Core\DependencyInjection\ServiceProviderInterface;
@@ -629,9 +628,9 @@ public function handle(Request $request, $type = self::MASTER_REQUEST, $catch =
       $this->initializeSettings($request);
 
       // Redirect the user to the installation script if Drupal has not been
-      // installed yet (i.e., if no $databases array has been defined in the
-      // settings.php file) and we are not already installing.
-      if (!Database::getConnectionInfo() && !drupal_installation_attempted() && PHP_SAPI !== 'cli') {
+      // installed yet, and we are not already installing, and we are not on the
+      // command line.
+      if (!drupal_installation_attempted() && PHP_SAPI !== 'cli' && !drupal_is_installed()) {
         $response = new RedirectResponse($request->getBasePath() . '/core/install.php');
       }
       else {