diff --git a/src/FileSystem/Filename.php b/src/FileSystem/Filename.php
index d2d7002..b1cd808 100644
--- a/src/FileSystem/Filename.php
+++ b/src/FileSystem/Filename.php
@@ -17,7 +17,7 @@ static public function fromString(string $filename = ''): self
             return new self('');
         }
 
-        if (str_starts_with($filename, '/') === false) {
+        if (str_starts_with($filename, DIRECTORY_SEPARATOR) === false) {
             $filename = DIRECTORY_SEPARATOR . $filename;
         }