use utils.escapeSystemdPath

backup.nix

@@ -1,4 +1,4 @@
-{ lib, config, pkgs, ... }:
+{ lib, config, pkgs, utils, ... }:
 let
   cfg = config.backup-helper;
   restic-wrapper = pkgs.writeShellApplication {
@@ -17,6 +17,7 @@ let
       # restic backup "$path";
     '';
   };
+  escaped-path = utils.escapeSystemdPath "/etc/machine-id";
 in
 {
   options.backup-helper.enable = lib.mkEnableOption "Enable backup-helper";
@@ -67,7 +68,7 @@ in
         RandomizedDelaySec = cfg.randomized-delay;
       };
     };
-    systemd.timers."backup-helper@/etc/machine-id" = {
+    systemd.timers.${escaped-path} = {
       wantedBy = [ "timers.target" ];
       overrideStrategy = "asDropin";
     };