diff --git a/src/Ftp/FtpAdapter.php b/src/Ftp/FtpAdapter.php
index 102fa0171..b15add8dc 100644
--- a/src/Ftp/FtpAdapter.php
+++ b/src/Ftp/FtpAdapter.php
@@ -27,6 +27,7 @@
 use League\MimeTypeDetection\MimeTypeDetector;
 use Throwable;
 
+use function array_map;
 use function error_clear_last;
 use function error_get_last;
 use function ftp_chdir;
@@ -489,7 +490,9 @@ private function normalizePermissions(string $permissions): int
 
         // convert the groups
         $mapper = static function ($part) {
-            return array_sum(str_split($part));
+            return array_sum(array_map(static function ($p) {
+                return (int) $p;
+            }, str_split($part)));
         };
 
         // converts to decimal number