diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 2c00a1f..762271f 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -10,6 +10,7 @@
 use Drupal\Core\PhpStorage\PhpStorageFactory;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Extension\ThemeHandlerInterface;
+use LogicException;
 
 /**
  * A class that defines a Twig environment for Drupal.
@@ -45,6 +46,10 @@ public function __construct(\Twig_LoaderInterface $loader = NULL, $options = arr
     // @todo Pass as arguments from the DIC.
     $this->cache_object = \Drupal::cache();
 
+    // Ensure that twig.engine is loaded, given that it is needed to render a
+    // template because functions like twig_drupal_escape_filter are called.
+    require_once 'core/themes/engines/twig/twig.engine';
+
     // Set twig path namespace for themes and modules.
     $namespaces = array();
     foreach ($module_handler->getModuleList() as $name => $extension) {
@@ -79,6 +84,9 @@ public function needsUpdate($cache_filename, $name) {
 
   /**
    * Compile the source and write the compiled template to disk.
+   *
+   * @param bool $inline
+   *   TRUE, if the $cache_filename is a rendered template.
    */
   public function updateCompiledTemplate($cache_filename, $name, $inline = FALSE) {
     $source = $this->getLoader($inline)->getSource($name);
@@ -89,6 +97,14 @@ public function updateCompiledTemplate($cache_filename, $name, $inline = FALSE)
     $this->cache_object->set($cid, REQUEST_TIME);
   }
 
+  /**
+   * Gets the Loader instance.
+   *
+   * @param bool $inline
+   *   TRUE, if the string loader is requested.
+   *
+   * @return \Twig_LoaderInterface A Twig_LoaderInterface instance
+   */
   public function getLoader($inline = FALSE) {
     if (NULL === $this->loader) {
       throw new LogicException('You must set a loader first.');
@@ -103,6 +119,21 @@ public function getLoader($inline = FALSE) {
    *
    * This is a straight copy from loadTemplate() changed to use
    * drupal_php_storage().
+   *
+   * @param string $name
+   *   The template name or the string which should be rendered as template.
+   * @param int $index
+   *   The index if it is an embedded template.
+   * @param bool $inline
+   *   TRUE, if the $name is a rendered template.
+   *
+   * @return \Twig_TemplateInterface
+   *   A template instance representing the given template name.
+   *
+   * @throws \Twig_Error_Loader
+   *   When the template cannot be found.
+   * @throws \Twig_Error_Syntax
+   *   When an error occurred during compilation.
    */
   public function loadTemplate($name, $index = NULL, $inline = FALSE) {
     $cls = $this->getTemplateClass($name, $index, $inline);
@@ -153,7 +184,17 @@ protected function storage() {
   }
 
   /**
-   * {@inheritdoc}
+   * Gets the template class associated with the given string.
+   *
+   * @param string $name
+   *   The name for which to calculate the template class name.
+   * @param int $index
+   *   The index if it is an embedded template.
+   * @param bool $inline
+   *   TRUE, if the $name is a rendered template.
+   *
+   * @return string
+   *   The template class name.
    */
   public function getTemplateClass($name, $index = NULL, $inline = FALSE) {
     // We override this method to add caching because it gets called multiple
diff --git a/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php b/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php
index f719bc6..7c100ed 100644
--- a/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php
@@ -10,9 +10,9 @@
 use Drupal\simpletest\KernelTestBase;
 
 /**
- * Tests the twig enviroment.
+ * Tests the twig environment.
  *
- * @see \Drupal\Core\Template\TwigEnviroment
+ * @see \Drupal\Core\Template\TwigEnvironment
  * @group Twig
  */
 class TwigEnvironmentTest extends KernelTestBase {