diff --git a/src/Cache/Delivery/CacheClearer.php b/src/Cache/Delivery/CacheClearer.php
index 496737a..eecbc02 100644
--- a/src/Cache/Delivery/CacheClearer.php
+++ b/src/Cache/Delivery/CacheClearer.php
@@ -31,7 +31,7 @@ public function __construct(Client $client, CacheItemPoolInterface $cacheItemPoo
         $this->clearer = new SdkCacheClearer($client, $client->getResourcePool(), $cacheItemPool);
     }
 
-    public function clear($cacheDir)
+    public function clear($cacheDir) : void
     {
         $this->clearer->clear();
     }