diff --git a/composer.json b/composer.json
index 97ad371..c8ab380 100644
--- a/composer.json
+++ b/composer.json
@@ -37,7 +37,7 @@
     "require-dev": {
         "ext-zend-opcache": "*",
         "ext-xdebug": "*",
-        "phpstan/phpstan": "^1.10",
+        "phpstan/phpstan": "^2.1",
         "phpunit/phpunit": "^10.3",
         "mockery/mockery": "^1.6",
         "league/flysystem-adapter-test-utilities": "^3.15",
diff --git a/src/CacheAdapter.php b/src/CacheAdapter.php
index 93d0c4c..38dabef 100644
--- a/src/CacheAdapter.php
+++ b/src/CacheAdapter.php
@@ -2,6 +2,7 @@
 
 namespace jgivoni\Flysystem\Cache;
 
+use ErrorException;
 use League\Flysystem\CalculateChecksumFromStream;
 use League\Flysystem\ChecksumAlgoIsNotSupported;
 use League\Flysystem\ChecksumProvider;
@@ -323,6 +324,11 @@ public function fileSize(string $path): FileAttributes
     public function checksum(string $path, Config $config): string
     {
         $algo = $config->get('checksum_algo');
+
+        if (isset($algo) && !is_string($algo)) {
+            throw new ErrorException('"checksum_algo" $config must be a string.');
+        }
+
         $metadataKey = isset($algo) ? 'checksum_' . $algo : 'checksum';
 
         $attributeAccessor = function (StorageAttributes $storageAttributes) use ($metadataKey) {
diff --git a/src/CacheItemsTrait.php b/src/CacheItemsTrait.php
index d262d20..4cbdb64 100644
--- a/src/CacheItemsTrait.php
+++ b/src/CacheItemsTrait.php
@@ -128,7 +128,6 @@ protected function getFileAttributes(
         $item = $this->getCacheItem($path);
 
         if ($item->isHit()) {
-            /** @var FileAttributes $fileAttributes */
             $fileAttributes = $item->get();
 
             if (!$fileAttributes instanceof FileAttributes) {