diff --git a/lib/Twig/Extension/Core.php b/lib/Twig/Extension/Core.php
index 3716f0248..f9ec2a475 100644
--- a/lib/Twig/Extension/Core.php
+++ b/lib/Twig/Extension/Core.php
@@ -885,6 +885,9 @@ function twig_split_filter(Twig_Environment $env, $value, $delimiter, $limit = n
 // The '_default' filter is used internally to avoid using the ternary operator
 // which costs a lot for big contexts (before PHP 5.4). So, on average,
 // a function call is cheaper.
+/**
+ * @internal
+ */
 function _twig_default_filter($value, $default = '')
 {
     if (twig_test_empty($value)) {
@@ -982,7 +985,9 @@ function twig_sort_filter($array)
     return $array;
 }
 
-/* used internally */
+/**
+ * @internal
+ */
 function twig_in_filter($value, $compare)
 {
     if (is_array($compare)) {
@@ -1150,7 +1155,9 @@ function twig_escape_filter(Twig_Environment $env, $string, $strategy = 'html',
     }
 }
 
-/* used internally */
+/**
+ * @internal
+ */
 function twig_escape_filter_is_safe(Twig_Node $filterArgs)
 {
     foreach ($filterArgs as $arg) {
@@ -1396,7 +1403,9 @@ else {
     }
 }
 
-/* used internally */
+/**
+ * @internal
+ */
 function twig_ensure_traversable($seq)
 {
     if ($seq instanceof Traversable || is_array($seq)) {
diff --git a/lib/Twig/Extension/Staging.php b/lib/Twig/Extension/Staging.php
index 8ab0f4596..583e6a911 100644
--- a/lib/Twig/Extension/Staging.php
+++ b/lib/Twig/Extension/Staging.php
@@ -15,6 +15,8 @@
  * This class is used by Twig_Environment as a staging area and must not be used directly.
  *
  * @author Fabien Potencier <fabien@symfony.com>
+ *
+ * @internal
  */
 class Twig_Extension_Staging extends Twig_Extension
 {
diff --git a/lib/Twig/Loader/String.php b/lib/Twig/Loader/String.php
index 9bfd856bf..00f507a4f 100644
--- a/lib/Twig/Loader/String.php
+++ b/lib/Twig/Loader/String.php
@@ -23,6 +23,8 @@
  *
  * @deprecated since 1.18.1 (to be removed in 2.0)
  *
+ * @internal
+ *
  * @author Fabien Potencier <fabien@symfony.com>
  */
 class Twig_Loader_String implements Twig_LoaderInterface, Twig_ExistsLoaderInterface
diff --git a/lib/Twig/Template.php b/lib/Twig/Template.php
index 36d41621a..a8160227e 100644
--- a/lib/Twig/Template.php
+++ b/lib/Twig/Template.php
@@ -61,6 +61,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @param array $context
      *
      * @return Twig_TemplateInterface|false The parent template or false if there is no parent
+     *
+     * @internal
      */
     public function getParent(array $context)
     {
@@ -111,6 +113,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @param string $name    The block name to display from the parent
      * @param array  $context The context
      * @param array  $blocks  The current set of blocks
+     *
+     * @internal
      */
     public function displayParentBlock($name, array $context, array $blocks = array())
     {
@@ -135,6 +139,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @param array  $context   The context
      * @param array  $blocks    The current set of blocks
      * @param bool   $useBlocks Whether to use the current set of blocks
+     *
+     * @internal
      */
     public function displayBlock($name, array $context, array $blocks = array(), $useBlocks = true)
     {
@@ -191,6 +197,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @param array  $blocks  The current set of blocks
      *
      * @return string The rendered block
+     *
+     * @internal
      */
     public function renderParentBlock($name, array $context, array $blocks = array())
     {
@@ -212,6 +220,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @param bool   $useBlocks Whether to use the current set of blocks
      *
      * @return string The rendered block
+     *
+     * @internal
      */
     public function renderBlock($name, array $context, array $blocks = array(), $useBlocks = true)
     {
@@ -237,6 +247,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @param string $name The block name
      *
      * @return bool true if the block exists, false otherwise
+     *
+     * @internal
      */
     public function hasBlock($name)
     {
@@ -252,6 +264,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @return array An array of block names
      *
      * @see hasBlock
+     *
+     * @internal
      */
     public function getBlockNames()
     {
@@ -298,6 +312,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @return array An array of blocks
      *
      * @see hasBlock
+     *
+     * @internal
      */
     public function getBlocks()
     {
@@ -407,6 +423,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      * @return mixed The content of the context variable
      *
      * @throws Twig_Error_Runtime if the variable does not exist and Twig is running in strict mode
+     *
+     * @internal
      */
     final protected function getContext($context, $item, $ignoreStrictCheck = false)
     {