diff --git a/src/Snowflake/Store/FileStore.php b/src/Snowflake/Store/FileStore.php
index 36b1e13..f00f80f 100644
--- a/src/Snowflake/Store/FileStore.php
+++ b/src/Snowflake/Store/FileStore.php
@@ -7,7 +7,8 @@
 
 class FileStore implements StoreInterface
 {
-    public function __construct($cacheDir)
+    private string $cacheDir;
+    public function __construct(string $cacheDir)
     {
         $this->cacheDir = $cacheDir;
 
diff --git a/src/Snowflake/Store/RedisStore.php b/src/Snowflake/Store/RedisStore.php
index 3f11e63..0e6aec4 100644
--- a/src/Snowflake/Store/RedisStore.php
+++ b/src/Snowflake/Store/RedisStore.php
@@ -7,10 +7,10 @@
 
 class RedisStore implements StoreInterface
 {
-    private $backend;
-    public function __construct(\Redis $redis)
+    private \Redis $backend;
+    public function __construct(\Redis $backend)
     {
-        $this->backend = $redis;
+        $this->backend = $backend;
     }
 
     private function getLuaScript()