diff --git a/includes/install.inc b/includes/install.inc
index 71de3e6..ff1d847 100644
--- a/includes/install.inc
+++ b/includes/install.inc
@@ -582,6 +582,29 @@ class DatabaseTaskException extends Exception {
 }
 
 /**
+ * Invalidates a PHP file from a possibly active opcode cache.
+ *
+ * In case the opcode cache does not support to invalidate an individual file,
+ * the entire cache will be flushed.
+ *
+ * @param string $pathname
+ *   The absolute pathname of the PHP file to invalidate.
+ */
+function drupal_clear_opcode_cache($pathname) {
+  clearstatcache(TRUE, $pathname);
+
+  if (extension_loaded('Zend OPcache')) {
+    opcache_invalidate($pathname, TRUE);
+  }
+  if (extension_loaded('apc')) {
+    // apc_delete_file() throws a PHP warning in case the specified file was
+    // not compiled yet.
+    // @see http://php.net/manual/en/function.apc-delete-file.php
+    @apc_delete_file($pathname);
+  }
+}
+
+/**
  * Replaces values in settings.php with values in the submitted array.
  *
  * @param $settings
@@ -653,6 +676,13 @@ function drupal_rewrite_settings($settings = array(), $prefix = '') {
     if ($fp && fwrite($fp, $buffer) === FALSE) {
       throw new Exception(st('Failed to modify %settings. Verify the file permissions.', array('%settings' => $settings_file)));
     }
+    else {
+      // The existing settings.php file might have been included already. In
+      // case an opcode cache is enabled, the rewritten contents of the file
+      // will not be reflected in this process. Ensure to invalidate the file
+      // in case an opcode cache is enabled.
+      drupal_clear_opcode_cache(DRUPAL_ROOT . '/' . $settings_file);
+    }
   }
   else {
     throw new Exception(st('Failed to open %settings. Verify the file permissions.', array('%settings' => $default_settings)));