diff --git a/src/Bootstrap/Bootstrap.php b/src/Bootstrap/Bootstrap.php
index b2627ea..94194c9 100644
--- a/src/Bootstrap/Bootstrap.php
+++ b/src/Bootstrap/Bootstrap.php
@@ -49,7 +49,7 @@ public function __construct(ConfigLoaderInterface $configLoader, DiContainerFact
         $this->diContainerFactory = $diContainerFactory;
     }
 
-    public function __invoke()
+    public function __invoke() : ContainerInterface
     {
         $this->loadConfig();
         $this->buildDiContainer();
diff --git a/src/Config/Config.php b/src/Config/Config.php
index 3e8329a..cb08ff8 100644
--- a/src/Config/Config.php
+++ b/src/Config/Config.php
@@ -19,7 +19,7 @@
  */
 class Config extends ArrayObject
 {
-    public static function fromArray(array $config)
+    public static function fromArray(array $config) : Config
     {
         return new self($config);
     }
diff --git a/src/Di/Container/Factory/AbstractFactory.php b/src/Di/Container/Factory/AbstractFactory.php
index 38ea914..a297027 100644
--- a/src/Di/Container/Factory/AbstractFactory.php
+++ b/src/Di/Container/Factory/AbstractFactory.php
@@ -49,11 +49,11 @@ public function __invoke(Config $config) : ContainerInterface
         return $container;
     }
 
-    abstract protected function createContainer();
+    abstract protected function createContainer() : ContainerInterface;
 
-    abstract protected function configure($container);
+    abstract protected function configure(ContainerInterface $container);
 
-    final protected function getConfig()
+    final protected function getConfig() : Config
     {
         return $this->config;
     }
diff --git a/src/Di/Container/Factory/AuraDiFactory.php b/src/Di/Container/Factory/AuraDiFactory.php
index 5b2a86f..acd1566 100644
--- a/src/Di/Container/Factory/AuraDiFactory.php
+++ b/src/Di/Container/Factory/AuraDiFactory.php
@@ -14,6 +14,7 @@
 
 use Aura\Di\Container;
 use Aura\Di\ContainerBuilder;
+use Interop\Container\ContainerInterface;
 
 /**
  * @author Nikola Posa <posa.nikola@gmail.com>
@@ -25,12 +26,12 @@ final class AuraDiFactory extends AbstractFactory
      */
     protected $container;
 
-    protected function createContainer()
+    protected function createContainer() : ContainerInterface
     {
         return (new ContainerBuilder())->newInstance();
     }
 
-    protected function configure($container)
+    protected function configure(ContainerInterface $container)
     {
         $this->container = $container;
         
diff --git a/src/Di/Container/Factory/PimpleFactory.php b/src/Di/Container/Factory/PimpleFactory.php
index 630310e..27a2a57 100644
--- a/src/Di/Container/Factory/PimpleFactory.php
+++ b/src/Di/Container/Factory/PimpleFactory.php
@@ -12,6 +12,7 @@
 
 namespace Phoundation\Di\Container\Factory;
 
+use Interop\Container\ContainerInterface;
 use Xtreamwayz\Pimple\Container;
 
 /**
@@ -24,12 +25,12 @@ final class PimpleFactory extends AbstractFactory
      */
     private $container;
 
-    protected function createContainer()
+    protected function createContainer() : ContainerInterface
     {
         return new Container();
     }
 
-    protected function configure($container)
+    protected function configure(ContainerInterface $container)
     {
         $this->container = $container;
 
diff --git a/src/Di/Container/Factory/ZendServiceManagerFactory.php b/src/Di/Container/Factory/ZendServiceManagerFactory.php
index 66de10d..46420f4 100644
--- a/src/Di/Container/Factory/ZendServiceManagerFactory.php
+++ b/src/Di/Container/Factory/ZendServiceManagerFactory.php
@@ -12,6 +12,7 @@
 
 namespace Phoundation\Di\Container\Factory;
 
+use Interop\Container\ContainerInterface;
 use Zend\ServiceManager\ServiceManager;
 
 /**
@@ -19,12 +20,12 @@
  */
 final class ZendServiceManagerFactory extends AbstractFactory
 {
-    protected function createContainer()
+    protected function createContainer() : ContainerInterface
     {
         return new ServiceManager();
     }
 
-    protected function configure($container)
+    protected function configure(ContainerInterface $container)
     {
         /* @var $container ServiceManager */