diff --git a/nixos/modules/services/mail/roundcube.nix b/nixos/modules/services/mail/roundcube.nix
index fe1eacafebbd..9a6ca6fa9635 100644
--- a/nixos/modules/services/mail/roundcube.nix
+++ b/nixos/modules/services/mail/roundcube.nix
@@ -190,6 +190,7 @@ in
             priority = 1100;
             extraConfig = ''
               add_header Cache-Control 'public, max-age=604800, must-revalidate';
+              client_max_body_size ${toString cfg.maxAttachmentSize};
             '';
           };
           locations."~ ^/(SQL|bin|config|logs|temp|vendor)/" = {