diff --git a/src/Composer/DevelopmentIntegrator.php b/src/Composer/DevelopmentIntegrator.php
index 9088bd9ce..c867eddd2 100644
--- a/src/Composer/DevelopmentIntegrator.php
+++ b/src/Composer/DevelopmentIntegrator.php
@@ -43,7 +43,7 @@ public static function integrate(Event $event)
         $event->getIO()->write('<fg=yellow>'.$process->getOutput().'</fg=yellow>');
     }
 
-    private static function noramlizePath($path): string
+    private static function noramlizePath(string $path): string
     {
         return strtr($path, '/', DIRECTORY_SEPARATOR);
     }
diff --git a/src/Composer/GrumPHPPlugin.php b/src/Composer/GrumPHPPlugin.php
index b91849d3d..5c286eef0 100644
--- a/src/Composer/GrumPHPPlugin.php
+++ b/src/Composer/GrumPHPPlugin.php
@@ -62,7 +62,7 @@ public function activate(Composer $composer, IOInterface $io)
      *
      * {@inheritdoc}
      */
-    public static function getSubscribedEvents()
+    public static function getSubscribedEvents(): array
     {
         return [
             PackageEvents::POST_PACKAGE_INSTALL => 'postPackageInstall',
diff --git a/src/Configuration/GrumPHP.php b/src/Configuration/GrumPHP.php
index 910cee7ac..ddf27db5b 100644
--- a/src/Configuration/GrumPHP.php
+++ b/src/Configuration/GrumPHP.php
@@ -122,7 +122,7 @@ public function getTestSuites(): TestSuiteCollection
      *
      * @return string|null
      */
-    public function getAsciiContentPath($resource)
+    public function getAsciiContentPath(string $resource)
     {
         $paths = $this->container->getParameter('ascii');
         if (!array_key_exists($resource, $paths)) {
diff --git a/src/Console/Application.php b/src/Console/Application.php
index 615bdac34..61d3e7c14 100644
--- a/src/Console/Application.php
+++ b/src/Console/Application.php
@@ -13,7 +13,9 @@
 use Monolog\Handler\StreamHandler;
 use Monolog\Logger;
 use Symfony\Component\Console\Application as SymfonyConsole;
+use Symfony\Component\Console\Helper\HelperSet;
 use Symfony\Component\Console\Input\ArgvInput;
+use Symfony\Component\Console\Input\InputDefinition;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\ConsoleOutput;
@@ -54,7 +56,7 @@ public function __construct()
         parent::__construct(self::APP_NAME, self::APP_VERSION);
     }
 
-    protected function getDefaultInputDefinition()
+    protected function getDefaultInputDefinition(): InputDefinition
     {
         $definition = parent::getDefaultInputDefinition();
         $definition->addOption(
@@ -70,7 +72,7 @@ protected function getDefaultInputDefinition()
         return $definition;
     }
 
-    protected function getDefaultCommands()
+    protected function getDefaultCommands(): array
     {
         $commands = parent::getDefaultCommands();
 
@@ -106,7 +108,7 @@ protected function getDefaultCommands()
         return $commands;
     }
 
-    protected function getDefaultHelperSet()
+    protected function getDefaultHelperSet(): HelperSet
     {
         $helperSet = parent::getDefaultHelperSet();
         $helperSet->set($this->initializeComposerHelper());
diff --git a/src/Console/Helper/PathsHelper.php b/src/Console/Helper/PathsHelper.php
index a8e9458bc..93da8efde 100644
--- a/src/Console/Helper/PathsHelper.php
+++ b/src/Console/Helper/PathsHelper.php
@@ -180,7 +180,7 @@ public function getBinDir(): string
      * Search a command in the bin folder
      * Note: the command locator is not injected because it needs the relative bin path.
      */
-    public function getBinCommand($command, $forceUnix = false): string
+    public function getBinCommand($command, bool $forceUnix = false): string
     {
         return $this->externalCommandLocator->locate($command, $forceUnix);
     }
@@ -188,7 +188,7 @@ public function getBinCommand($command, $forceUnix = false): string
     /**
      * @throws FileNotFoundException If file doesn't exists
      */
-    public function getRelativePath($path): string
+    public function getRelativePath(string $path): string
     {
         $realpath = $this->getAbsolutePath($path);
 
diff --git a/src/Console/Helper/TaskRunnerHelper.php b/src/Console/Helper/TaskRunnerHelper.php
index a9ac54298..d61a07211 100644
--- a/src/Console/Helper/TaskRunnerHelper.php
+++ b/src/Console/Helper/TaskRunnerHelper.php
@@ -132,7 +132,7 @@ private function returnWarningMessages(OutputInterface $output, array $warningMe
     /**
      * {@inheritdoc}
      */
-    public function getName()
+    public function getName(): string
     {
         return self::HELPER_NAME;
     }
diff --git a/src/Locator/ConfigurationFile.php b/src/Locator/ConfigurationFile.php
index 892e3317c..bee0c93bd 100644
--- a/src/Locator/ConfigurationFile.php
+++ b/src/Locator/ConfigurationFile.php
@@ -45,7 +45,7 @@ public function locate(string $workingDir, PackageInterface $package = null): st
         return $defaultPath;
     }
 
-    private function useConfigPathFromComposer(PackageInterface $package, $defaultPath): string
+    private function useConfigPathFromComposer(PackageInterface $package, string $defaultPath): string
     {
         $extra = $package->getExtra();
         if (!isset($extra['grumphp']['config-default-path'])) {
@@ -57,7 +57,7 @@ private function useConfigPathFromComposer(PackageInterface $package, $defaultPa
         return $this->locateConfigFileWithDistSupport($composerDefaultPath);
     }
 
-    private function locateConfigFileWithDistSupport($defaultPath): string
+    private function locateConfigFileWithDistSupport(string $defaultPath): string
     {
         $distPath = ('.dist' !== strpos($defaultPath, -5)) ? $defaultPath.'.dist' : $defaultPath;
         if ($this->filesystem->exists($defaultPath) || !$this->filesystem->exists($distPath)) {
diff --git a/src/Parser/Php/Configurator/TraverserConfigurator.php b/src/Parser/Php/Configurator/TraverserConfigurator.php
index c839e196a..1bdce7600 100644
--- a/src/Parser/Php/Configurator/TraverserConfigurator.php
+++ b/src/Parser/Php/Configurator/TraverserConfigurator.php
@@ -59,11 +59,9 @@ public function registerVisitorId(string $alias, string $visitorId)
     }
 
     /**
-     * @param array|null $visitorOptions
-     *
      * @throws \GrumPHP\Exception\RuntimeException
      */
-    public function registerStandardEnabledVisitor($alias, array $visitorOptions = null)
+    public function registerStandardEnabledVisitor(string $alias, array $visitorOptions = null)
     {
         if (array_key_exists($alias, $this->standardEnabledVisitors)) {
             throw new RuntimeException(
diff --git a/src/Process/ProcessFactory.php b/src/Process/ProcessFactory.php
index 36882cb22..716712d29 100644
--- a/src/Process/ProcessFactory.php
+++ b/src/Process/ProcessFactory.php
@@ -12,7 +12,7 @@
  */
 final class ProcessFactory
 {
-    public static function fromArguments(ProcessArgumentsCollection $arguments)
+    public static function fromArguments(ProcessArgumentsCollection $arguments): Process
     {
         // @todo Remove backward compatibility layer as soon as Symfony Process accepts an array (3.3+).
         //       From then on, you can simply pass `$arguments->getValues()` directly as the first constructor argument.
diff --git a/src/Util/Regex.php b/src/Util/Regex.php
index 2d8d23850..203b632ce 100644
--- a/src/Util/Regex.php
+++ b/src/Util/Regex.php
@@ -22,7 +22,7 @@ class Regex
     /**
      * Regex constructor.
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
         $this->regex = $this->toRegex($string);
     }