diff --git a/src/Fs.php b/src/Fs.php
index 4d69468..2014768 100644
--- a/src/Fs.php
+++ b/src/Fs.php
@@ -141,7 +141,7 @@ protected static function client(array $config = []): S3Client
      */
     protected function addFileMetadataToConfig(array $config): array
     {
-        if (DateTimeHelper::isValidIntervalString($this->expires)) {
+        if ($this->expires && DateTimeHelper::isValidIntervalString($this->expires)) {
             $expires = new DateTime();
             $now = new DateTime();
             $expires->modify('+' . $this->expires);