diff --git a/PVE/API2/Backup.pm b/PVE/API2/Backup.pm
index 3bd8559..a890c1f 100644
--- a/PVE/API2/Backup.pm
+++ b/PVE/API2/Backup.pm
@@ -259,6 +259,7 @@ __PACKAGE__->register_method({
                 type => 'string',
                 description => "Job ID (will be autogenerated).",
                 format => 'pve-configid',
+                maxLength => 50,
                 optional => 1, # FIXME: make required on 8.0
             },
             schedule => {