diff --git a/Controller/StreamController.php b/Controller/StreamController.php
index f96e664..49940fa 100644
--- a/Controller/StreamController.php
+++ b/Controller/StreamController.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Debril\RssAtomBundle\Controller;
 
@@ -28,7 +28,7 @@ class StreamController extends Controller
      * @return Response
      * @throws \Exception
      */
-    public function indexAction(Request $request, FeedContentProviderInterface $provider, FeedIo $feedIo)
+    public function indexAction(Request $request, FeedContentProviderInterface $provider, FeedIo $feedIo) : Response
     {
         $options = $request->attributes->get('_route_params');
         $this->setModifiedSince($request);
@@ -47,7 +47,7 @@ public function indexAction(Request $request, FeedContentProviderInterface $prov
      *
      * @return \DateTime
      */
-    protected function getModifiedSince()
+    protected function getModifiedSince() : \DateTime
     {
         if (is_null($this->since)) {
             $this->since = new \DateTime('@0');
@@ -61,7 +61,7 @@ protected function getModifiedSince()
      *
      * @return $this
      */
-    protected function setModifiedSince(Request $request)
+    protected function setModifiedSince(Request $request) : self
     {
         $this->since = new \DateTime();
         if ($request->headers->has('If-Modified-Since')) {
@@ -88,7 +88,7 @@ protected function setModifiedSince(Request $request)
      *
      * @throws \Exception
      */
-    protected function createStreamResponse(array $options, $format, FeedContentProviderInterface $provider, FeedIo $feedIo)
+    protected function createStreamResponse(array $options, string $format, FeedContentProviderInterface $provider, FeedIo $feedIo) : Response
     {
         $content = $this->getContent($options, $provider);
 
@@ -110,7 +110,7 @@ protected function createStreamResponse(array $options, $format, FeedContentProv
      * @param string $format
      * @return $this
      */
-    protected function setFeedHeaders(Response $response, FeedInterface $feed, $format)
+    protected function setFeedHeaders(Response $response, FeedInterface $feed, string $format) : self
     {
         $contentType =
             'json' == $format ?
@@ -140,7 +140,7 @@ protected function setFeedHeaders(Response $response, FeedInterface $feed, $form
      *
      * @throws \Exception
      */
-    protected function getContent(array $options, $provider)
+    protected function getContent(array $options, FeedContentProviderInterface $provider) : FeedInterface
     {
         try {
             return $provider->getFeedContent($options);
@@ -154,7 +154,7 @@ protected function getContent(array $options, $provider)
      *
      * @return bool
      */
-    protected function mustForceRefresh()
+    protected function mustForceRefresh() : bool
     {
         return $this->container->getParameter('debril_rss_atom.force_refresh');
     }
@@ -162,7 +162,7 @@ protected function mustForceRefresh()
     /**
      * @return boolean true if the feed must be private
      */
-    protected function isPrivate()
+    protected function isPrivate() : bool
     {
         return $this->container->getParameter('debril_rss_atom.private_feeds');
     }
diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 1bc7b99..4fe4f80 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Debril\RssAtomBundle\DependencyInjection;
 
@@ -15,7 +15,7 @@ class Configuration implements ConfigurationInterface
     /**
      * {@inheritDoc}
      */
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder() : TreeBuilder
     {
         $treeBuilder = new TreeBuilder();
 
diff --git a/DependencyInjection/DebrilRssAtomExtension.php b/DependencyInjection/DebrilRssAtomExtension.php
index 7d23e14..bbfb255 100644
--- a/DependencyInjection/DebrilRssAtomExtension.php
+++ b/DependencyInjection/DebrilRssAtomExtension.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Debril\RssAtomBundle\DependencyInjection;
 
@@ -36,7 +36,7 @@ class DebrilRssAtomExtension extends Extension implements CompilerPassInterface
     /**
      * {@inheritDoc}
      */
-    public function load(array $configs, ContainerBuilder $container)
+    public function load(array $configs, ContainerBuilder $container) : void
     {
         $configuration = new Configuration();
         $config = $this->processConfiguration($configuration, $configs);
@@ -56,7 +56,7 @@ public function load(array $configs, ContainerBuilder $container)
      * @param array $config
      * @return $this
      */
-    protected function setDateFormats(ContainerBuilder $container, array $config)
+    protected function setDateFormats(ContainerBuilder $container, array $config) : self
     {
         $dateFormats = isset($config['date_formats']) ?
             array_merge($this->defaultDateFormats, $config['date_formats']):
@@ -71,20 +71,20 @@ protected function setDateFormats(ContainerBuilder $container, array $config)
     }
 
     /**
-     * @param ContainerBuilder $builder
+     * @param ContainerBuilder $container
      */
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container) : void
     {
         $this->setDefinition($container, 'logger', 'Psr\Log\NullLogger');
     }
 
     /**
      * @param ContainerBuilder $container
-     * @param $serviceName
-     * @param $className
-     * @return $this
+     * @param string $serviceName
+     * @param string $className
+     * @return DebrilRssAtomExtension
      */
-    protected function setDefinition(ContainerBuilder $container, $serviceName, $className)
+    protected function setDefinition(ContainerBuilder $container, string $serviceName, string $className) : self
     {
         if ( ! $container->has($serviceName) ) {
             $container->setDefinition($serviceName, new Definition($className));
diff --git a/Provider/DoctrineFeedContentProvider.php b/Provider/DoctrineFeedContentProvider.php
index a308c4f..1d0ce5b 100644
--- a/Provider/DoctrineFeedContentProvider.php
+++ b/Provider/DoctrineFeedContentProvider.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /**
  * Feed aggregator for Symfony.
@@ -42,7 +42,7 @@ public function __construct(Registry $doctrine)
      *
      * @return string
      */
-    public function getRepositoryName()
+    public function getRepositoryName() : string
     {
         return $this->repositoryName;
     }
@@ -54,7 +54,7 @@ public function getRepositoryName()
      *
      * @return DoctrineFeedContentProvider
      */
-    public function setRepositoryName($repositoryName)
+    public function setRepositoryName(string $repositoryName) : self
     {
         $this->repositoryName = $repositoryName;
 
@@ -68,7 +68,7 @@ public function setRepositoryName($repositoryName)
      *
      * @throws FeedNotFoundException
      */
-    public function getFeedContent(array $options)
+    public function getFeedContent(array $options) : FeedInterface
     {
         // fetch feed from data repository
         $feed = $this->getDoctrine()
@@ -96,9 +96,9 @@ public function getDoctrine()
     /**
      * @param array $options
      *
-     * @return mixed
+     * @return string
      */
-    public function getIdFromOptions(array $options)
+    public function getIdFromOptions(array $options) : string
     {
         $optionsResolver = new OptionsResolver();
         $optionsResolver->setRequired('id');
diff --git a/Provider/FeedContentProviderInterface.php b/Provider/FeedContentProviderInterface.php
index 4b0bbda..b9ba3e9 100644
--- a/Provider/FeedContentProviderInterface.php
+++ b/Provider/FeedContentProviderInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /**
  * RssAtomBundle.
@@ -26,5 +26,5 @@ interface FeedContentProviderInterface
      *
      * @return FeedInterface
      */
-    public function getFeedContent(array $options);
+    public function getFeedContent(array $options) : FeedInterface;
 }
diff --git a/Provider/MockProvider.php b/Provider/MockProvider.php
index 6d135a5..6806cbe 100644
--- a/Provider/MockProvider.php
+++ b/Provider/MockProvider.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /**
  * RssAtomBundle.
@@ -14,6 +14,7 @@
 use FeedIo\Feed;
 use FeedIo\Feed\Item;
 use Debril\RssAtomBundle\Exception\FeedException\FeedNotFoundException;
+use FeedIo\FeedInterface;
 
 /**
  * Class MockProvider.
@@ -23,11 +24,11 @@ class MockProvider implements FeedContentProviderInterface
     /**
      * @param array $options
      *
-     * @return Feed
+     * @return FeedInterface
      *
      * @throws FeedNotFoundException
      */
-    public function getFeedContent(array $options)
+    public function getFeedContent(array $options) : FeedInterface
     {
         $feed = new Feed();
 
@@ -51,7 +52,7 @@ public function getFeedContent(array $options)
      * @param Feed $feed
      * @return Feed
      */
-    protected function addItem(Feed $feed)
+    protected function addItem(Feed $feed) : FeedInterface
     {
         $item = new Item();
 
diff --git a/Tests/Provider/MockProviderTest.php b/Tests/Provider/MockProviderTest.php
index f361544..59374f2 100644
--- a/Tests/Provider/MockProviderTest.php
+++ b/Tests/Provider/MockProviderTest.php
@@ -34,7 +34,7 @@ protected function tearDown()
      */
     public function testGetContent()
     {
-        $options = array('id' => 1);
+        $options = array('id' => 'some id');
         $feed = $this->object->getFeedContent($options);
 
         $this->assertInstanceOf('FeedIo\FeedInterface', $feed);