diff --git a/src/Symfony/Bridge/Twig/Command/DebugCommand.php b/src/Symfony/Bridge/Twig/Command/DebugCommand.php
index bb37d99b21..6100eb87a5 100644
--- a/src/Symfony/Bridge/Twig/Command/DebugCommand.php
+++ b/src/Symfony/Bridge/Twig/Command/DebugCommand.php
@@ -149,7 +149,7 @@ EOF
                     return;
                 }
                 $refl = new \ReflectionMethod($cb[0], $cb[1]);
-            } elseif (is_object($cb) && is_callable($cb)) {
+            } elseif (is_object($cb) && method_exists($cb, '__invoke')) {
                 $refl = new \ReflectionMethod($cb, '__invoke');
             } elseif (function_exists($cb)) {
                 $refl = new \ReflectionFunction($cb);
diff --git a/src/Symfony/Bundle/FrameworkBundle/Resources/config/debug_prod.xml b/src/Symfony/Bundle/FrameworkBundle/Resources/config/debug_prod.xml
index 4078a656d5..3ef3ec90d0 100644
--- a/src/Symfony/Bundle/FrameworkBundle/Resources/config/debug_prod.xml
+++ b/src/Symfony/Bundle/FrameworkBundle/Resources/config/debug_prod.xml
@@ -12,7 +12,7 @@
         <service id="debug.debug_handlers_listener" class="Symfony\Component\HttpKernel\EventListener\DebugHandlersListener">
             <tag name="kernel.event_subscriber" />
             <tag name="monolog.logger" channel="php" />
-            <argument /><!-- Exception handler -->
+            <argument>null</argument><!-- Exception handler -->
             <argument type="service" id="logger" on-invalid="null" />
             <argument>null</argument><!-- Log levels map for enabled error levels -->
             <argument>null</argument>
diff --git a/src/Symfony/Component/Console/Helper/ProcessHelper.php b/src/Symfony/Component/Console/Helper/ProcessHelper.php
index fab23ee0d4..2c46a2c39d 100644
--- a/src/Symfony/Component/Console/Helper/ProcessHelper.php
+++ b/src/Symfony/Component/Console/Helper/ProcessHelper.php
@@ -36,7 +36,7 @@ class ProcessHelper extends Helper
      *
      * @return Process The process that ran
      */
-    public function run(OutputInterface $output, $cmd, $error = null, $callback = null, $verbosity = OutputInterface::VERBOSITY_VERY_VERBOSE)
+    public function run(OutputInterface $output, $cmd, $error = null, callable $callback = null, $verbosity = OutputInterface::VERBOSITY_VERY_VERBOSE)
     {
         if ($output instanceof ConsoleOutputInterface) {
             $output = $output->getErrorOutput();
@@ -92,7 +92,7 @@ class ProcessHelper extends Helper
      *
      * @see run()
      */
-    public function mustRun(OutputInterface $output, $cmd, $error = null, $callback = null)
+    public function mustRun(OutputInterface $output, $cmd, $error = null, callable $callback = null)
     {
         $process = $this->run($output, $cmd, $error, $callback);
 
@@ -112,7 +112,7 @@ class ProcessHelper extends Helper
      *
      * @return callable
      */
-    public function wrapCallback(OutputInterface $output, Process $process, $callback = null)
+    public function wrapCallback(OutputInterface $output, Process $process, callable $callback = null)
     {
         if ($output instanceof ConsoleOutputInterface) {
             $output = $output->getErrorOutput();
diff --git a/src/Symfony/Component/Console/Helper/ProgressBar.php b/src/Symfony/Component/Console/Helper/ProgressBar.php
index 099f45420a..59127f943a 100644
--- a/src/Symfony/Component/Console/Helper/ProgressBar.php
+++ b/src/Symfony/Component/Console/Helper/ProgressBar.php
@@ -86,7 +86,7 @@ class ProgressBar
      * @param string   $name     The placeholder name (including the delimiter char like %)
      * @param callable $callable A PHP callable
      */
-    public static function setPlaceholderFormatterDefinition($name, $callable)
+    public static function setPlaceholderFormatterDefinition($name, callable $callable)
     {
         if (!self::$formatters) {
             self::$formatters = self::initPlaceholderFormatters();
diff --git a/src/Symfony/Component/Console/Helper/QuestionHelper.php b/src/Symfony/Component/Console/Helper/QuestionHelper.php
index b95bf9e5f5..13ea0d0834 100644
--- a/src/Symfony/Component/Console/Helper/QuestionHelper.php
+++ b/src/Symfony/Component/Console/Helper/QuestionHelper.php
@@ -377,7 +377,7 @@ class QuestionHelper extends Helper
      *
      * @throws \Exception In case the max number of attempts has been reached and no valid response has been given
      */
-    private function validateAttempts($interviewer, OutputInterface $output, Question $question)
+    private function validateAttempts(callable $interviewer, OutputInterface $output, Question $question)
     {
         $error = null;
         $attempts = $question->getMaxAttempts();
diff --git a/src/Symfony/Component/Console/Question/Question.php b/src/Symfony/Component/Console/Question/Question.php
index 9aa4c69d27..71cb8f5c8b 100644
--- a/src/Symfony/Component/Console/Question/Question.php
+++ b/src/Symfony/Component/Console/Question/Question.php
@@ -164,7 +164,7 @@ class Question
      *
      * @return Question The current instance
      */
-    public function setValidator($validator)
+    public function setValidator(callable $validator = null)
     {
         $this->validator = $validator;
 
@@ -220,11 +220,11 @@ class Question
      *
      * The normalizer can be a callable (a string), a closure or a class implementing __invoke.
      *
-     * @param string|\Closure $normalizer
+     * @param callable $normalizer
      *
      * @return Question The current instance
      */
-    public function setNormalizer($normalizer)
+    public function setNormalizer(callable $normalizer)
     {
         $this->normalizer = $normalizer;
 
@@ -236,7 +236,7 @@ class Question
      *
      * The normalizer can ba a callable (a string), a closure or a class implementing __invoke.
      *
-     * @return string|\Closure
+     * @return callable
      */
     public function getNormalizer()
     {
diff --git a/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php b/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php
index 7222261cd5..c42f29f609 100644
--- a/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php
+++ b/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php
@@ -41,7 +41,7 @@ class ExpressionFunction
      * @param callable $compiler  A callable able to compile the function
      * @param callable $evaluator A callable able to evaluate the function
      */
-    public function __construct($name, $compiler, $evaluator)
+    public function __construct($name, callable $compiler, callable $evaluator)
     {
         $this->name = $name;
         $this->compiler = $compiler;
diff --git a/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php b/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php
index fb3faf79a5..e40afd00ed 100644
--- a/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php
+++ b/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php
@@ -112,7 +112,7 @@ class ExpressionLanguage
      *
      * @see ExpressionFunction
      */
-    public function register($name, $compiler, $evaluator)
+    public function register($name, callable $compiler, callable $evaluator)
     {
         $this->functions[$name] = array('compiler' => $compiler, 'evaluator' => $evaluator);
     }
diff --git a/src/Symfony/Component/Finder/Iterator/CustomFilterIterator.php b/src/Symfony/Component/Finder/Iterator/CustomFilterIterator.php
index 24b15d97ad..b43b88d98d 100644
--- a/src/Symfony/Component/Finder/Iterator/CustomFilterIterator.php
+++ b/src/Symfony/Component/Finder/Iterator/CustomFilterIterator.php
@@ -26,8 +26,8 @@ class CustomFilterIterator extends FilterIterator
     /**
      * Constructor.
      *
-     * @param \Iterator $iterator The Iterator to filter
-     * @param array     $filters  An array of PHP callbacks
+     * @param \Iterator  $iterator The Iterator to filter
+     * @param callable[] $filters  An array of PHP callbacks
      *
      * @throws \InvalidArgumentException
      */
diff --git a/src/Symfony/Component/Form/ChoiceList/ArrayKeyChoiceList.php b/src/Symfony/Component/Form/ChoiceList/ArrayKeyChoiceList.php
index 7c3c107d0f..55cfab399f 100644
--- a/src/Symfony/Component/Form/ChoiceList/ArrayKeyChoiceList.php
+++ b/src/Symfony/Component/Form/ChoiceList/ArrayKeyChoiceList.php
@@ -101,7 +101,7 @@ class ArrayKeyChoiceList extends ArrayChoiceList
      *                                  the keys of the values or if any of the
      *                                  choices is not scalar
      */
-    public function __construct($choices, $value = null)
+    public function __construct($choices, callable $value = null)
     {
         // If no values are given, use the choices as values
         // Since the choices are stored in the collection keys, i.e. they are
diff --git a/src/Symfony/Component/Form/ChoiceList/LazyChoiceList.php b/src/Symfony/Component/Form/ChoiceList/LazyChoiceList.php
index f691d71330..27d8deb882 100644
--- a/src/Symfony/Component/Form/ChoiceList/LazyChoiceList.php
+++ b/src/Symfony/Component/Form/ChoiceList/LazyChoiceList.php
@@ -59,7 +59,7 @@ class LazyChoiceList implements ChoiceListInterface
      * @param null|callable         $value  The callable generating the choice
      *                                      values
      */
-    public function __construct(ChoiceLoaderInterface $loader, $value = null)
+    public function __construct(ChoiceLoaderInterface $loader, callable $value = null)
     {
         $this->loader = $loader;
         $this->value = $value;
diff --git a/src/Symfony/Component/HttpFoundation/StreamedResponse.php b/src/Symfony/Component/HttpFoundation/StreamedResponse.php
index 90c272b469..b021d3c405 100644
--- a/src/Symfony/Component/HttpFoundation/StreamedResponse.php
+++ b/src/Symfony/Component/HttpFoundation/StreamedResponse.php
@@ -36,7 +36,7 @@ class StreamedResponse extends Response
      * @param int           $status   The response status code
      * @param array         $headers  An array of response headers
      */
-    public function __construct($callback = null, $status = 200, $headers = array())
+    public function __construct(callable $callback = null, $status = 200, $headers = array())
     {
         parent::__construct(null, $status, $headers);
 
diff --git a/src/Symfony/Component/HttpKernel/Controller/ControllerResolver.php b/src/Symfony/Component/HttpKernel/Controller/ControllerResolver.php
index 1af46dc656..a4a5fdba14 100644
--- a/src/Symfony/Component/HttpKernel/Controller/ControllerResolver.php
+++ b/src/Symfony/Component/HttpKernel/Controller/ControllerResolver.php
@@ -131,7 +131,7 @@ class ControllerResolver implements ControllerResolverInterface
      *
      * @param string $controller A Controller string
      *
-     * @return mixed A PHP callable
+     * @return callable A PHP callable
      *
      * @throws \InvalidArgumentException
      */
diff --git a/src/Symfony/Component/HttpKernel/Event/FilterControllerEvent.php b/src/Symfony/Component/HttpKernel/Event/FilterControllerEvent.php
index 93c9553fd4..e0af13106c 100644
--- a/src/Symfony/Component/HttpKernel/Event/FilterControllerEvent.php
+++ b/src/Symfony/Component/HttpKernel/Event/FilterControllerEvent.php
@@ -29,12 +29,10 @@ class FilterControllerEvent extends KernelEvent
 {
     /**
      * The current controller.
-     *
-     * @var callable
      */
     private $controller;
 
-    public function __construct(HttpKernelInterface $kernel, $controller, Request $request, $requestType)
+    public function __construct(HttpKernelInterface $kernel, callable $controller, Request $request, $requestType)
     {
         parent::__construct($kernel, $request, $requestType);
 
diff --git a/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php b/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php
index f50e4d6c3b..33a543819d 100644
--- a/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php
+++ b/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php
@@ -45,7 +45,7 @@ class DebugHandlersListener implements EventSubscriberInterface
      * @param bool                 $scream           Enables/disables screaming mode, where even silenced errors are logged
      * @param string               $fileLinkFormat   The format for links to source files
      */
-    public function __construct($exceptionHandler, LoggerInterface $logger = null, $levels = null, $throwAt = -1, $scream = true, $fileLinkFormat = null)
+    public function __construct(callable $exceptionHandler = null, LoggerInterface $logger = null, $levels = null, $throwAt = -1, $scream = true, $fileLinkFormat = null)
     {
         $this->exceptionHandler = $exceptionHandler;
         $this->logger = $logger;
diff --git a/src/Symfony/Component/HttpKernel/Tests/HttpKernelTest.php b/src/Symfony/Component/HttpKernel/Tests/HttpKernelTest.php
index 97e68f66f9..06f611ef46 100644
--- a/src/Symfony/Component/HttpKernel/Tests/HttpKernelTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/HttpKernelTest.php
@@ -154,17 +154,6 @@ class HttpKernelTest extends \PHPUnit_Framework_TestCase
         $kernel->handle(new Request());
     }
 
-    /**
-     * @expectedException \LogicException
-     */
-    public function testHandleWhenTheControllerIsNotACallable()
-    {
-        $dispatcher = new EventDispatcher();
-        $kernel = new HttpKernel($dispatcher, $this->getResolver('foobar'));
-
-        $kernel->handle(new Request());
-    }
-
     public function testHandleWhenTheControllerIsAClosure()
     {
         $response = new Response('foo');
diff --git a/src/Symfony/Component/Process/PhpProcess.php b/src/Symfony/Component/Process/PhpProcess.php
index e5777ea22a..583516bbbe 100644
--- a/src/Symfony/Component/Process/PhpProcess.php
+++ b/src/Symfony/Component/Process/PhpProcess.php
@@ -54,7 +54,7 @@ class PhpProcess extends Process
     /**
      * {@inheritdoc}
      */
-    public function start($callback = null)
+    public function start(callable $callback = null)
     {
         if (null === $this->getCommandLine()) {
             throw new RuntimeException('Unable to find the PHP executable.');
diff --git a/src/Symfony/Component/Process/Process.php b/src/Symfony/Component/Process/Process.php
index 02499cb208..3a369fd3bf 100644
--- a/src/Symfony/Component/Process/Process.php
+++ b/src/Symfony/Component/Process/Process.php
@@ -217,7 +217,7 @@ class Process
      * @throws RuntimeException       if PHP was compiled with --enable-sigchild and the enhanced sigchild compatibility mode is not enabled
      * @throws ProcessFailedException if the process didn't terminate successfully
      */
-    public function mustRun($callback = null)
+    public function mustRun(callable $callback = null)
     {
         if ($this->isSigchildEnabled() && !$this->enhanceSigchildCompatibility) {
             throw new RuntimeException('This PHP has been compiled with --enable-sigchild. You must use setEnhanceSigchildCompatibility() to use this method.');
@@ -252,7 +252,7 @@ class Process
      * @throws RuntimeException When process is already running
      * @throws LogicException   In case a callback is provided and output has been disabled
      */
-    public function start($callback = null)
+    public function start(callable $callback = null)
     {
         if ($this->isRunning()) {
             throw new RuntimeException('Process is already running');
@@ -310,7 +310,7 @@ class Process
      *
      * @see start()
      */
-    public function restart($callback = null)
+    public function restart(callable $callback = null)
     {
         if ($this->isRunning()) {
             throw new RuntimeException('Process is already running');
@@ -337,7 +337,7 @@ class Process
      * @throws RuntimeException When process stopped after receiving signal
      * @throws LogicException   When process is not yet started
      */
-    public function wait($callback = null)
+    public function wait(callable $callback = null)
     {
         $this->requireProcessIsStarted(__FUNCTION__);
 
@@ -1232,7 +1232,7 @@ class Process
      *
      * @param callable|null $callback The user defined PHP callback
      *
-     * @return callable A PHP callable
+     * @return \Closure A PHP closure
      */
     protected function buildCallback($callback)
     {
diff --git a/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
index a39e8896d7..4bc71ca667 100644
--- a/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
@@ -97,7 +97,7 @@ abstract class AbstractNormalizer extends SerializerAwareNormalizer implements N
     /**
      * Set normalization callbacks.
      *
-     * @param array $callbacks help normalize the result
+     * @param callable[] $callbacks help normalize the result
      *
      * @return self
      *
diff --git a/src/Symfony/Component/Templating/PhpEngine.php b/src/Symfony/Component/Templating/PhpEngine.php
index de90d74aad..50b3956648 100644
--- a/src/Symfony/Component/Templating/PhpEngine.php
+++ b/src/Symfony/Component/Templating/PhpEngine.php
@@ -350,10 +350,10 @@ class PhpEngine implements EngineInterface, \ArrayAccess
     /**
      * Adds an escaper for the given context.
      *
-     * @param string $context The escaper context (html, js, ...)
-     * @param mixed  $escaper A PHP callable
+     * @param string   $context The escaper context (html, js, ...)
+     * @param callable $escaper A PHP callable
      */
-    public function setEscaper($context, $escaper)
+    public function setEscaper($context, callable $escaper)
     {
         $this->escapers[$context] = $escaper;
         self::$escaperCache[$context] = array();
@@ -364,7 +364,7 @@ class PhpEngine implements EngineInterface, \ArrayAccess
      *
      * @param string $context The context name
      *
-     * @return mixed $escaper A PHP callable
+     * @return callable $escaper A PHP callable
      *
      * @throws \InvalidArgumentException
      */
diff --git a/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php b/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php
index 79817803a2..c7f035de23 100644
--- a/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php
+++ b/src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php
@@ -304,7 +304,7 @@ abstract class AbstractCloner implements ClonerInterface
                 $a = $cast;
             }
         } catch (\Exception $e) {
-            $a[(Stub::TYPE_OBJECT === $stub->type ? Caster::PREFIX_VIRTUAL : '').'⚠'] = new ThrowingCasterException($callback, $e);
+            $a[(Stub::TYPE_OBJECT === $stub->type ? Caster::PREFIX_VIRTUAL : '').'⚠'] = new ThrowingCasterException($e);
         }
 
         return $a;
diff --git a/src/Symfony/Component/VarDumper/Exception/ThrowingCasterException.php b/src/Symfony/Component/VarDumper/Exception/ThrowingCasterException.php
index c1b427b92e..976f4439b6 100644
--- a/src/Symfony/Component/VarDumper/Exception/ThrowingCasterException.php
+++ b/src/Symfony/Component/VarDumper/Exception/ThrowingCasterException.php
@@ -17,10 +17,9 @@ namespace Symfony\Component\VarDumper\Exception;
 class ThrowingCasterException extends \Exception
 {
     /**
-     * @param callable   $caster The failing caster
-     * @param \Exception $prev   The exception thrown from the caster
+     * @param \Exception $prev The exception thrown from the caster
      */
-    public function __construct($caster, \Exception $prev)
+    public function __construct(\Exception $prev)
     {
         parent::__construct('Unexpected '.get_class($prev).' thrown from a caster: '.$prev->getMessage(), 0, $prev);
     }
diff --git a/src/Symfony/Component/VarDumper/VarDumper.php b/src/Symfony/Component/VarDumper/VarDumper.php
index c728439df2..8c610c5d33 100644
--- a/src/Symfony/Component/VarDumper/VarDumper.php
+++ b/src/Symfony/Component/VarDumper/VarDumper.php
@@ -38,12 +38,8 @@ class VarDumper
         return call_user_func(self::$handler, $var);
     }
 
-    public static function setHandler($callable)
+    public static function setHandler(callable $callable = null)
     {
-        if (null !== $callable && !is_callable($callable, true)) {
-            throw new \InvalidArgumentException('Invalid PHP callback.');
-        }
-
         $prevHandler = self::$handler;
         self::$handler = $callable;