diff --git a/src/Exchanger.php b/src/Exchanger.php
index aa06e07..42cf6ac 100755
--- a/src/Exchanger.php
+++ b/src/Exchanger.php
@@ -56,7 +56,7 @@ final class Exchanger implements ExchangeRateProviderContract
      * @param CacheInterface|null         $cache
      * @param array                       $options
      */
-    public function __construct(ExchangeRateServiceContract $service, CacheInterface $cache = null, array $options = [])
+    public function __construct(ExchangeRateServiceContract $service, ?CacheInterface $cache = null, array $options = [])
     {
         $this->service = $service;
         $this->cache = $cache;
diff --git a/src/Service/HttpService.php b/src/Service/HttpService.php
index c24daf0..d6a5d6c 100644
--- a/src/Service/HttpService.php
+++ b/src/Service/HttpService.php
@@ -47,7 +47,7 @@ abstract class HttpService extends Service
      * @param RequestFactoryInterface|null    $requestFactory
      * @param array                           $options
      */
-    public function __construct($httpClient = null, RequestFactoryInterface $requestFactory = null, array $options = [])
+    public function __construct($httpClient = null, ?RequestFactoryInterface $requestFactory = null, array $options = [])
     {
         if (null === $httpClient) {
             $httpClient = HttpClientDiscovery::find();