diff -u b/core/includes/install.core.inc b/core/includes/install.core.inc
--- b/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1019,7 +1019,7 @@
   $driver = $form_state['values']['driver'];
   $database = $form_state['values'][$driver];
   $drivers = drupal_get_database_types();
-  if ($drivers[$driver]->isCustom()) {
+  if (substr(get_class($drivers[$driver]), 0, 11) !== 'Drupal\\Core') {
     $database['custom'] = TRUE;
   }
   $database['driver'] = $driver;
diff -u b/core/lib/Drupal/Core/Database/Database.php b/core/lib/Drupal/Core/Database/Database.php
--- b/core/lib/Drupal/Core/Database/Database.php
+++ b/core/lib/Drupal/Core/Database/Database.php
@@ -369,6 +369,7 @@
     if (!isset(self::$databaseInfo[$key])) {
       throw new ConnectionNotDefinedException('The specified database connection is not defined: ' . $key);
     }
+
     if (!$driver = self::$databaseInfo[$key][$target]['driver']) {
       throw new DriverNotSpecifiedException('Driver not specified for this database connection: ' . $key);
     }
reverted:
--- b/core/lib/Drupal/Core/Database/Install/Tasks.php
+++ a/core/lib/Drupal/Core/Database/Install/Tasks.php
@@ -302,13 +302,4 @@
     return $errors;
   }
 
-  /**
-   * Core driver?
-   *
-   * @return
-   *   TRUE if this is a custom driver, FALSE if the driver is in core.
-   */
-  public function isCustom() {
-    return FALSE;
-  }
 }