diff --git a/services/prebuild.nix b/services/prebuild.nix
index 6ed7f94..527ef75 100644
--- a/services/prebuild.nix
+++ b/services/prebuild.nix
@@ -1,39 +1,59 @@
-# services/prebuild.nix — nightly pre-build of the Macbook's system closure.
+# services/prebuild.nix — nightly pre-build of the other hosts' system closures.
 #
-# The Macbook runs with max-jobs = 0 and offloads every build to this host
-# (nix.buildMachines in common.nix). Realising its toplevel here ahead of time
-# turns `update` on the laptop into a pure copy: the offloaded build finds the
-# path already in this store and just ships it back over SSH.
+# Both laptops/desktops offload builds to this host (nix.buildMachines in
+# common.nix), and the Macbook can't build at all (max-jobs = 0). Realising
+# their toplevels here ahead of time turns `update` on those machines into a
+# pure copy: the offloaded build finds the path already in this store and just
+# ships it back over SSH.
 #
-# --out-link doubles as the gc root, so `clean` doesn't reap the closure
-# before the laptop ever asks for it.
+# --out-link doubles as the gc root, so `clean` doesn't reap the closures
+# before the other machines ever ask for them.
 { config, lib, pkgs, ... }:
 
+let
+  mkService = host: {
+    description = "Pre-build the ${host} system closure";
+    after = [ "network-online.target" ];
+    wants = [ "network-online.target" ];
+    path = [ pkgs.git ];
+    environment.HOME = "/root";
+    serviceConfig = {
+      Type = "oneshot";
+      StateDirectory = "prebuild";
+    };
+    # Gaming's kernel comes from lantian's attic (see hosts/hardware/
+    # FredOS-Gaming.nix). That substituter isn't configured on this host, so
+    # without it the cachyos kernel gets built from source here instead of
+    # fetched — hours, not minutes. Harmless for the Macbook.
+    script = ''
+      ${config.nix.package}/bin/nix build --refresh \
+        --option extra-substituters https://attic.xuyh0120.win/lantian \
+        --option extra-trusted-public-keys lantian:EeAUQ+W+6r7EtwnmYjeVwx5kOGEBpjlBfPlzGlTNvHc= \
+        --out-link /var/lib/prebuild/${host} \
+        'git+https://forg.gregersen.it/rope/nixos#nixosConfigurations.${host}.config.system.build.toplevel'
+    '';
+  };
+
+  # Staggered so the two builds don't fight over cores and bandwidth.
+  mkTimer = startAt: {
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnCalendar = startAt;
+      Persistent = true;
+      RandomizedDelaySec = "20m";
+    };
+  };
+in
 {
   config = lib.mkIf (config.networking.hostName == "FredOS-Mediaserver") {
-    systemd.services.prebuild-macbook = {
-      description = "Pre-build the FredOS-Macbook system closure";
-      after = [ "network-online.target" ];
-      wants = [ "network-online.target" ];
-      path = [ pkgs.git ];
-      environment.HOME = "/root";
-      serviceConfig = {
-        Type = "oneshot";
-        StateDirectory = "prebuild";
-      };
-      script = ''
-        ${config.nix.package}/bin/nix build --refresh --out-link /var/lib/prebuild/FredOS-Macbook \
-          'git+https://forg.gregersen.it/rope/nixos#nixosConfigurations.FredOS-Macbook.config.system.build.toplevel'
-      '';
+    systemd.services = {
+      prebuild-macbook = mkService "FredOS-Macbook";
+      prebuild-gaming = mkService "FredOS-Gaming";
     };
 
-    systemd.timers.prebuild-macbook = {
-      wantedBy = [ "timers.target" ];
-      timerConfig = {
-        OnCalendar = "04:00";
-        Persistent = true;
-        RandomizedDelaySec = "30m";
-      };
+    systemd.timers = {
+      prebuild-macbook = mkTimer "04:00";
+      prebuild-gaming = mkTimer "05:00";
     };
   };
 }