If it's present. Particularly useful for nix-os users who install Emacs+vterm with this statement: systemPackages = with pkgs; [ ((emacsPackagesNgGen emacs).emacsWithPackages (epkgs: [ epkgs.emacs-libvterm ])) ]; Or with home-manager: programs.emacs = { enable = true; extraPackages = epkgs: [ epkgs.emacs-libvterm ]; };