diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 9b3d7a0..2af108e 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1103,18 +1103,41 @@ function install_settings_form($form, &$form_state, &$install_state) {
 
   $conf_path = './' . conf_path(FALSE);
   $settings_file = $conf_path . '/settings.php';
-  $database = isset($databases['default']['default']) ? $databases['default']['default'] : array();
 
   drupal_set_title(t('Database configuration'));
 
   $drivers = drupal_get_database_types();
   $drivers_keys = array_keys($drivers);
 
+  // If database connection settings have been prepared in settings.php already,
+  // then the existing values need to be taken over.
+  // Note: The installer even executes this form if there is a valid database
+  // connection already, since the submit handler of this form is responsible
+  // for writing all $settings to settings.php (not limited to $databases).
+  if (isset($databases['default']['default'])) {
+    $default_driver = $databases['default']['default']['driver'];
+    $default_options = $databases['default']['default'];
+  }
+  // Otherwise, use the database connection settings from the form input.
+  // For a non-interactive installation, this is derived from the original
+  // $settings array passed into install_drupal().
+  elseif (isset($form_state['input']['driver'])) {
+    $default_driver = $form_state['input']['driver'];
+    $default_options = $form_state['input'][$default_driver];
+  }
+  // If there is no database information at all yet, just suggest the first
+  // available driver as default value, so that its settings form is made
+  // visible via #states when JavaScript is enabled (see below).
+  else {
+    $default_driver = current($drivers_keys);
+    $default_options = array();
+  }
+
   $form['driver'] = array(
     '#type' => 'radios',
     '#title' => t('Database type'),
     '#required' => TRUE,
-    '#default_value' => !empty($database['driver']) ? $database['driver'] : current($drivers_keys),
+    '#default_value' => $default_driver,
   );
   if (count($drivers) == 1) {
     $form['driver']['#disabled'] = TRUE;
@@ -1124,7 +1147,7 @@ function install_settings_form($form, &$form_state, &$install_state) {
   foreach ($drivers as $key => $driver) {
     $form['driver']['#options'][$key] = $driver->name();
 
-    $form['settings'][$key] = $driver->getFormOptions($database);
+    $form['settings'][$key] = $driver->getFormOptions($default_options);
     $form['settings'][$key]['#prefix'] = '<h2 class="js-hide">' . t('@driver_name settings', array('@driver_name' => $driver->name())) . '</h2>';
     $form['settings'][$key]['#type'] = 'container';
     $form['settings'][$key]['#tree'] = TRUE;
@@ -1143,7 +1166,7 @@ function install_settings_form($form, &$form_state, &$install_state) {
     '#button_type' => 'primary',
     '#limit_validation_errors' => array(
       array('driver'),
-      array(isset($form_state['input']['driver']) ? $form_state['input']['driver'] : current($drivers_keys)),
+      array($default_driver),
     ),
     '#submit' => array('install_settings_form_submit'),
   );