diff --git a/src/HttpClientPool.php b/src/HttpClientPool.php
index 7ac292c..c51d044 100644
--- a/src/HttpClientPool.php
+++ b/src/HttpClientPool.php
@@ -5,6 +5,7 @@
 use Http\Client\Common\Exception\HttpClientNotFoundException;
 use Http\Client\HttpAsyncClient;
 use Http\Client\HttpClient;
+use Psr\Http\Client\ClientInterface;
 use Psr\Http\Message\RequestInterface;
 
 /**
@@ -21,7 +22,7 @@ abstract class HttpClientPool implements HttpAsyncClient, HttpClient
     /**
      * Add a client to the pool.
      *
-     * @param HttpClient|HttpAsyncClient|HttpClientPoolItem $client
+     * @param HttpClient|HttpAsyncClient|HttpClientPoolItem|ClientInterface $client
      */
     public function addHttpClient($client)
     {
diff --git a/src/HttpClientPoolItem.php b/src/HttpClientPoolItem.php
index 09cd6dd..5c79137 100644
--- a/src/HttpClientPoolItem.php
+++ b/src/HttpClientPoolItem.php
@@ -4,6 +4,7 @@
 
 use Http\Client\HttpAsyncClient;
 use Http\Client\HttpClient;
+use Psr\Http\Client\ClientInterface;
 use Psr\Http\Message\RequestInterface;
 use Http\Client\Exception;
 
@@ -38,7 +39,7 @@ class HttpClientPoolItem implements HttpClient, HttpAsyncClient
     private $client;
 
     /**
-     * @param HttpClient|HttpAsyncClient $client
+     * @param HttpClient|HttpAsyncClient|ClientInterface $client
      * @param null|int                   $reenableAfter Number of seconds after this client is reenable
      */
     public function __construct($client, $reenableAfter = null)
diff --git a/src/HttpClientRouter.php b/src/HttpClientRouter.php
index 9f72133..8f897d2 100644
--- a/src/HttpClientRouter.php
+++ b/src/HttpClientRouter.php
@@ -6,6 +6,7 @@
 use Http\Client\HttpAsyncClient;
 use Http\Client\HttpClient;
 use Http\Message\RequestMatcher;
+use Psr\Http\Client\ClientInterface;
 use Psr\Http\Message\RequestInterface;
 
 /**
@@ -43,7 +44,7 @@ public function sendAsyncRequest(RequestInterface $request)
     /**
      * Add a client to the router.
      *
-     * @param HttpClient|HttpAsyncClient $client
+     * @param HttpClient|HttpAsyncClient|ClientInterface $client
      * @param RequestMatcher             $requestMatcher
      */
     public function addClient($client, RequestMatcher $requestMatcher)
@@ -59,7 +60,7 @@ public function addClient($client, RequestMatcher $requestMatcher)
      *
      * @param RequestInterface $request
      *
-     * @return HttpClient|HttpAsyncClient
+     * @return HttpClient|HttpAsyncClient|ClientInterface
      */
     protected function chooseHttpClient(RequestInterface $request)
     {
diff --git a/src/PluginClient.php b/src/PluginClient.php
index 8cedcf6..c90ddcf 100644
--- a/src/PluginClient.php
+++ b/src/PluginClient.php
@@ -41,7 +41,7 @@ final class PluginClient implements HttpClient, HttpAsyncClient
     private $options;
 
     /**
-     * @param HttpClient|HttpAsyncClient $client
+     * @param HttpClient|HttpAsyncClient|ClientInterface $client
      * @param Plugin[]                   $plugins
      * @param array                      $options {
      *