diff --git a/src/Symfony/Component/Debug/Debug.php b/src/Symfony/Component/Debug/Debug.php
index 5d2d55cf9f021..329d50c7e3e50 100644
--- a/src/Symfony/Component/Debug/Debug.php
+++ b/src/Symfony/Component/Debug/Debug.php
@@ -28,7 +28,7 @@ class Debug
      * @param int  $errorReportingLevel The level of error reporting you want
      * @param bool $displayErrors       Whether to display errors (for development) or just log them (for production)
      */
-    public static function enable($errorReportingLevel = E_ALL, $displayErrors = true)
+    public static function enable(int $errorReportingLevel = E_ALL, bool $displayErrors = true)
     {
         if (static::$enabled) {
             return;
diff --git a/src/Symfony/Component/Debug/DebugClassLoader.php b/src/Symfony/Component/Debug/DebugClassLoader.php
index ff9a8d72f903f..0bee58783af1d 100644
--- a/src/Symfony/Component/Debug/DebugClassLoader.php
+++ b/src/Symfony/Component/Debug/DebugClassLoader.php
@@ -129,9 +129,9 @@ public static function disable()
     }
 
     /**
-     * @return string|null
+     * @param string $class
      */
-    public function findFile($class)
+    public function findFile(string $class)
     {
         return $this->isFinder ? $this->classLoader[0]->findFile($class) ?: null : null;
     }
@@ -139,11 +139,9 @@ public function findFile($class)
     /**
      * Loads the given class or interface.
      *
-     * @param string $class The name of the class
-     *
      * @throws \RuntimeException
      */
-    public function loadClass($class)
+    public function loadClass(string $class)
     {
         $e = error_reporting(error_reporting() | E_PARSE | E_ERROR | E_CORE_ERROR | E_COMPILE_ERROR);
 
diff --git a/src/Symfony/Component/Debug/ErrorHandler.php b/src/Symfony/Component/Debug/ErrorHandler.php
index a99a000b07fa9..bfe948713f743 100644
--- a/src/Symfony/Component/Debug/ErrorHandler.php
+++ b/src/Symfony/Component/Debug/ErrorHandler.php
@@ -176,7 +176,7 @@ public function __construct(BufferingLogger $bootstrappingLogger = null)
      * @param array|int       $levels  An array map of E_* to LogLevel::* or an integer bit field of E_* constants
      * @param bool            $replace Whether to replace or not any existing logger
      */
-    public function setDefaultLogger(LoggerInterface $logger, $levels = E_ALL, $replace = false)
+    public function setDefaultLogger(LoggerInterface $logger, $levels = E_ALL, bool $replace = false)
     {
         $loggers = [];
 
@@ -526,7 +526,7 @@ public function handleError($type, $message, $file, $line)
      *
      * @internal
      */
-    public function handleException($exception, array $error = null)
+    public function handleException(\Throwable $exception, array $error = null)
     {
         if (null === $error) {
             self::$exitCode = 255;
diff --git a/src/Symfony/Component/Debug/Exception/FlattenException.php b/src/Symfony/Component/Debug/Exception/FlattenException.php
index eaed1f1fa6f90..d371a16a90ff9 100644
--- a/src/Symfony/Component/Debug/Exception/FlattenException.php
+++ b/src/Symfony/Component/Debug/Exception/FlattenException.php
@@ -103,7 +103,7 @@ public function getStatusCode()
     /**
      * @return $this
      */
-    public function setStatusCode($code)
+    public function setStatusCode(int $code)
     {
         $this->statusCode = $code;
 
@@ -133,7 +133,7 @@ public function getClass()
     /**
      * @return $this
      */
-    public function setClass($class)
+    public function setClass(string $class)
     {
         $this->class = 'c' === $class[0] && 0 === strpos($class, "class@anonymous\0") ? get_parent_class($class).'@anonymous' : $class;
 
@@ -148,7 +148,7 @@ public function getFile()
     /**
      * @return $this
      */
-    public function setFile($file)
+    public function setFile(string $file)
     {
         $this->file = $file;
 
@@ -163,7 +163,7 @@ public function getLine()
     /**
      * @return $this
      */
-    public function setLine($line)
+    public function setLine(int $line)
     {
         $this->line = $line;
 
@@ -178,7 +178,7 @@ public function getMessage()
     /**
      * @return $this
      */
-    public function setMessage($message)
+    public function setMessage(string $message)
     {
         if (false !== strpos($message, "class@anonymous\0")) {
             $message = preg_replace_callback('/class@anonymous\x00.*?\.php0x?[0-9a-fA-F]++/', function ($m) {
@@ -199,7 +199,7 @@ public function getCode()
     /**
      * @return $this
      */
-    public function setCode($code)
+    public function setCode(int $code)
     {
         $this->code = $code;
 
@@ -257,7 +257,7 @@ public function setTraceFromThrowable(\Throwable $throwable)
     /**
      * @return $this
      */
-    public function setTrace($trace, $file, $line)
+    public function setTrace(array $trace, string $file, int $line)
     {
         $this->trace = [];
         $this->trace[] = [
@@ -294,7 +294,7 @@ public function setTrace($trace, $file, $line)
         return $this;
     }
 
-    private function flattenArgs($args, $level = 0, &$count = 0)
+    private function flattenArgs(array $args, int $level = 0, int &$count = 0)
     {
         $result = [];
         foreach ($args as $key => $value) {
diff --git a/src/Symfony/Component/Debug/ExceptionHandler.php b/src/Symfony/Component/Debug/ExceptionHandler.php
index e36610c82e14a..5bea8a5f1cbf1 100644
--- a/src/Symfony/Component/Debug/ExceptionHandler.php
+++ b/src/Symfony/Component/Debug/ExceptionHandler.php
@@ -60,11 +60,11 @@ public function __construct(bool $debug = true, string $charset = null, $fileLin
      *
      * @param bool        $debug          Enable/disable debug mode, where the stack trace is displayed
      * @param string|null $charset        The charset used by exception messages
-     * @param string|null $fileLinkFormat The IDE link template
+     * @param string|FileLinkFormatter|null $fileLinkFormat The IDE link template
      *
      * @return static
      */
-    public static function register($debug = true, $charset = null, $fileLinkFormat = null)
+    public static function register(bool $debug = true, string $charset = null, $fileLinkFormat = null)
     {
         $handler = new static($debug, $charset, $fileLinkFormat);