diff --git a/sl-src/Cache.php b/sl-src/Cache.php
index 3fb3e1d4..ec1ae732 100644
--- a/sl-src/Cache.php
+++ b/sl-src/Cache.php
@@ -30,9 +30,9 @@ final class Cache
     /** @var string  */
     private $tmpDir;
 
-    public function __construct($tmpDir)
+    public function __construct(string $tmpDir)
     {
-        $this->tmpDir =  $tmpDir;
+        $this->tmpDir = $tmpDir;
     }
 
     /**