diff --git a/doc/advanced.rst b/doc/advanced.rst
index 5c25aea66..398bffb65 100644
--- a/doc/advanced.rst
+++ b/doc/advanced.rst
@@ -360,7 +360,7 @@ This is used by many of the tests built into Twig::
 
     class OddTestExpression extends TestExpression
     {
-        public function compile(\Twig\Compiler $compiler)
+        public function compile(\Twig\Compiler $compiler): void
         {
             $compiler
                 ->raw('(')
@@ -473,7 +473,7 @@ Now, let's see the actual code of this class::
 
     class CustomSetTokenParser extends \Twig\TokenParser\AbstractTokenParser
     {
-        public function parse(\Twig\Token $token)
+        public function parse(\Twig\Token $token): Node
         {
             $parser = $this->parser;
             $stream = $parser->getStream();
@@ -486,7 +486,7 @@ Now, let's see the actual code of this class::
             return new CustomSetNode($name, $value, $token->getLine(), $this->getTag());
         }
 
-        public function getTag()
+        public function getTag(): string
         {
             return 'set';
         }
@@ -535,7 +535,7 @@ The ``CustomSetNode`` class itself is quite short::
             parent::__construct(['value' => $value], ['name' => $name], $line, $tag);
         }
 
-        public function compile(\Twig\Compiler $compiler)
+        public function compile(\Twig\Compiler $compiler): void
         {
             $compiler
                 ->addDebugInfo($this)
@@ -597,42 +597,42 @@ An extension is a class that implements the following interface::
          *
          * @return \Twig\TokenParser\TokenParserInterface[]
          */
-        public function getTokenParsers();
+        public function getTokenParsers(): array
 
         /**
          * Returns the node visitor instances to add to the existing list.
          *
          * @return \Twig\NodeVisitor\NodeVisitorInterface[]
          */
-        public function getNodeVisitors();
+        public function getNodeVisitors(): array
 
         /**
          * Returns a list of filters to add to the existing list.
          *
          * @return \Twig\TwigFilter[]
          */
-        public function getFilters();
+        public function getFilters(): array
 
         /**
          * Returns a list of tests to add to the existing list.
          *
          * @return \Twig\TwigTest[]
          */
-        public function getTests();
+        public function getTests(): array
 
         /**
          * Returns a list of functions to add to the existing list.
          *
          * @return \Twig\TwigFunction[]
          */
-        public function getFunctions();
+        public function getFunctions(): array
 
         /**
          * Returns a list of operators to add to the existing list.
          *
          * @return array<array> First array of unary operators, second array of binary operators
          */
-        public function getOperators();
+        public function getOperators(): array
     }
 
 To keep your extension class clean and lean, inherit from the built-in
@@ -684,7 +684,7 @@ method::
 
     class CustomTwigExtension extends \Twig\Extension\AbstractExtension
     {
-        public function getFunctions()
+        public function getFunctions(): array
         {
             return [
                 new \Twig\TwigFunction('lipsum', 'generate_lipsum'),
@@ -703,7 +703,7 @@ environment::
 
     class CustomTwigExtension extends \Twig\Extension\AbstractExtension
     {
-        public function getFilters()
+        public function getFilters(): array
         {
             return [
                 new \Twig\TwigFilter('rot13', 'str_rot13'),
@@ -722,7 +722,7 @@ to the Twig environment::
 
     class CustomTwigExtension extends \Twig\Extension\AbstractExtension
     {
-        public function getTokenParsers()
+        public function getTokenParsers(): array
         {
             return [new CustomSetTokenParser()];
         }
@@ -742,7 +742,7 @@ the ``!``, ``||``, and ``&&`` operators::
 
     class CustomTwigExtension extends \Twig\Extension\AbstractExtension
     {
-        public function getOperators()
+        public function getOperators(): array
         {
             return [
                 [
@@ -765,7 +765,7 @@ The ``getTests()`` method lets you add new test functions::
 
     class CustomTwigExtension extends \Twig\Extension\AbstractExtension
     {
-        public function getTests()
+        public function getTests(): array
         {
             return [
                 new \Twig\TwigTest('even', 'twig_test_even'),
@@ -801,14 +801,14 @@ The simplest way to use methods is to define them on the extension itself::
             $this->rot13Provider = $rot13Provider;
         }
 
-        public function getFunctions()
+        public function getFunctions(): array
         {
             return [
                 new \Twig\TwigFunction('rot13', [$this, 'rot13']),
             ];
         }
 
-        public function rot13($value)
+        public function rot13($value): string
         {
             return $this->rot13Provider->rot13($value);
         }
@@ -825,7 +825,7 @@ must be autoload-able)::
 
     class RuntimeLoader implements \Twig\RuntimeLoader\RuntimeLoaderInterface
     {
-        public function load($class)
+        public function load($class): void
         {
             // implement the logic to create an instance of $class
             // and inject its dependencies
@@ -857,7 +857,7 @@ It is now possible to move the runtime logic to a new
             $this->rot13Provider = $rot13Provider;
         }
 
-        public function rot13($value)
+        public function rot13($value): string
         {
             return $this->rot13Provider->rot13($value);
         }
@@ -865,7 +865,7 @@ It is now possible to move the runtime logic to a new
 
     class CustomTwigExtension extends \Twig\Extension\AbstractExtension
     {
-        public function getFunctions()
+        public function getFunctions(): array
         {
             return [
                 new \Twig\TwigFunction('rot13', ['CustomRuntimeExtension', 'rot13']),
diff --git a/doc/api.rst b/doc/api.rst
index 219bdec33..6a5dd39d2 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -253,11 +253,9 @@ All loaders implement the ``\Twig\Loader\LoaderInterface``::
          *
          * @param string $name The template logical name
          *
-         * @return \Twig\Source
-         *
          * @throws \Twig\Error\LoaderError When $name is not found
          */
-        public function getSourceContext($name);
+        public function getSourceContext($name): \Twig\Source;
 
         /**
          * Gets the cache key to use for the cache for a given template name.
@@ -268,7 +266,7 @@ All loaders implement the ``\Twig\Loader\LoaderInterface``::
          *
          * @throws \Twig\Error\LoaderError When $name is not found
          */
-        public function getCacheKey($name);
+        public function getCacheKey($name): string;
 
         /**
          * Returns true if the template is still fresh.
@@ -280,7 +278,7 @@ All loaders implement the ``\Twig\Loader\LoaderInterface``::
          *
          * @throws \Twig\Error\LoaderError When $name is not found
          */
-        public function isFresh($name, $time);
+        public function isFresh($name, $time): bool;
 
         /**
          * Check if we have the source code of a template, given its name.
@@ -289,7 +287,7 @@ All loaders implement the ``\Twig\Loader\LoaderInterface``::
          *
          * @return bool    If the template source code is handled by this loader or not
          */
-        public function exists($name);
+        public function exists($name): bool;
     }
 
 The ``isFresh()`` method must return ``true`` if the current cached template
diff --git a/doc/recipes.rst b/doc/recipes.rst
index 7febe3e55..fe39afab7 100644
--- a/doc/recipes.rst
+++ b/doc/recipes.rst
@@ -370,7 +370,7 @@ Now, let's define a loader able to use this database::
             return new \Twig\Source($source, $name);
         }
 
-        public function exists(string $name)
+        public function exists(string $name): bool
         {
             return $name === $this->getValue('name', $name);
         }
diff --git a/src/Loader/LoaderInterface.php b/src/Loader/LoaderInterface.php
index fec7e85ff..5bccbef80 100644
--- a/src/Loader/LoaderInterface.php
+++ b/src/Loader/LoaderInterface.php
@@ -42,8 +42,5 @@ interface LoaderInterface
      */
     public function isFresh(string $name, int $time): bool;
 
-    /**
-     * @return bool
-     */
-    public function exists(string $name);
+    public function exists(string $name): bool;
 }
diff --git a/src/RuntimeLoader/ContainerRuntimeLoader.php b/src/RuntimeLoader/ContainerRuntimeLoader.php
index 36435ea2d..6646cfbaa 100644
--- a/src/RuntimeLoader/ContainerRuntimeLoader.php
+++ b/src/RuntimeLoader/ContainerRuntimeLoader.php
@@ -30,7 +30,7 @@ class ContainerRuntimeLoader implements RuntimeLoaderInterface
         $this->container = $container;
     }
 
-    public function load(string $class)
+    public function load(string $class): ?object
     {
         return $this->container->has($class) ? $this->container->get($class) : null;
     }
diff --git a/src/RuntimeLoader/FactoryRuntimeLoader.php b/src/RuntimeLoader/FactoryRuntimeLoader.php
index 6aad95caf..5adfa395d 100644
--- a/src/RuntimeLoader/FactoryRuntimeLoader.php
+++ b/src/RuntimeLoader/FactoryRuntimeLoader.php
@@ -31,7 +31,7 @@ class FactoryRuntimeLoader implements RuntimeLoaderInterface
         $this->map = $map;
     }
 
-    public function load(string $class)
+    public function load(string $class): ?object
     {
         if (!isset($this->map[$class])) {
             return null;
diff --git a/src/RuntimeLoader/RuntimeLoaderInterface.php b/src/RuntimeLoader/RuntimeLoaderInterface.php
index 9e5b2048e..9d7d96d8e 100644
--- a/src/RuntimeLoader/RuntimeLoaderInterface.php
+++ b/src/RuntimeLoader/RuntimeLoaderInterface.php
@@ -23,5 +23,5 @@ interface RuntimeLoaderInterface
      *
      * @return object|null The runtime instance or null if the loader does not know how to create the runtime for this class
      */
-    public function load(string $class);
+    public function load(string $class): ?object;
 }