diff --git a/src/Gaufrette/Adapter/AsyncAwsS3.php b/src/Gaufrette/Adapter/AsyncAwsS3.php
index 972cdf38..06f5daa2 100644
--- a/src/Gaufrette/Adapter/AsyncAwsS3.php
+++ b/src/Gaufrette/Adapter/AsyncAwsS3.php
@@ -314,6 +314,9 @@ protected function computeKey(string $path): string
         return ltrim(substr($path, strlen($this->options['directory'])), '/');
     }
 
+    /**
+     * @param string|resource $content
+     */
     private function guessContentType(mixed $content): bool|string
     {
         $fileInfo = new \finfo(FILEINFO_MIME_TYPE);