diff --git a/devices/servivi/modules/binary-cache.nix b/devices/servivi/modules/binary-cache.nix
index 8d5a8a0b..1e744369 100644
--- a/devices/servivi/modules/binary-cache.nix
+++ b/devices/servivi/modules/binary-cache.nix
@@ -1,35 +1,24 @@
 {
   config,
   mainUser,
-  nix-eval-jobs,
-  nix-fast-build,
   pkgs,
   ...
 }: let
-  # FIXME: move nix-fast-build-pkg to overlays, make #nixFastChecks an attrset of all, packages, devices and aptDevices. add binary cache at apartment
+  # FIXME: make #nixFastChecks an attrset of all, packages, devices and aptDevices
+  #        add binary cache at apartment
+  inherit (builtins) attrValues;
   inherit (config.sops) secrets;
 
-  nix-fast-build-pkg = nix-fast-build.packages.${pkgs.system}.nix-fast-build.override {
-    nix-eval-jobs =
-      nix-eval-jobs.packages.${pkgs.system}.default.override {
-        nix = config.nix.package;
-      }
-      // {
-        nix = config.nix.package;
-      };
-  };
-
   nixFastBuild = pkgs.writeShellApplication {
     name = "nixFastBuild";
 
-    runtimeInputs = builtins.attrValues {
+    runtimeInputs = attrValues {
       inherit
         (pkgs)
         gnugrep
+        nix-fast-build
         nix-output-monitor
         ;
-
-      inherit nix-fast-build-pkg;
     };
 
     text = ''
@@ -45,11 +34,10 @@
 in {
   services.nix-serve = {
     enable = true;
-    package = pkgs.nix-serve-ng;
     secretKeyFile = secrets.binary-cache-key.path;
   };
 
-  environment.systemPackages = [nix-fast-build-pkg nixFastBuild];
+  environment.systemPackages = [pkgs.nix-fast-build nixFastBuild];
 
   # Populate cache
   systemd = {
@@ -60,17 +48,16 @@ in {
         Group = config.users.users.${mainUser}.group;
       };
 
-      path = builtins.attrValues {
+      path = attrValues {
         inherit
           (pkgs)
           bash
           git
+          nix-fast-build
           openssh
           ;
 
         inherit (config.nix) package;
-
-        inherit nix-fast-build-pkg;
       };
 
       script = ''
diff --git a/outputs.nix b/outputs.nix
index 879555ab..de40520e 100644
--- a/outputs.nix
+++ b/outputs.nix
@@ -134,7 +134,7 @@
       perSystem (pkgs:
         import ./packages {inherit inputs mkVersion pkgs;});
 
-    overlays = import ./overlays {};
+    overlays = import ./overlays {inherit self;};
 
     apps =
       perSystem (pkgs:
diff --git a/overlays/default.nix b/overlays/default.nix
index 11060335..e78db738 100644
--- a/overlays/default.nix
+++ b/overlays/default.nix
@@ -1,5 +1,5 @@
-{...}: {
+{self, ...}: {
   build-failures = import ./build-failures;
-  nix-version = import ./nix-version;
+  nix-version = import ./nix-version self;
   xdg-desktop-portal-kde = import ./xdg-desktop-portal-kde;
 }
diff --git a/overlays/nix-version/default.nix b/overlays/nix-version/default.nix
index 762bfe9f..148200b8 100644
--- a/overlays/nix-version/default.nix
+++ b/overlays/nix-version/default.nix
@@ -1,15 +1,26 @@
-{nix ? null}: (
-  final: prev:
-    builtins.mapAttrs
-    (n: v:
-      if nix == null
-      then prev.${n}
-      else v)
-    {
-      inherit nix;
+self: {nix ? null}: final: prev: let
+  inherit (builtins) mapAttrs;
+  inherit (self.inputs) nix-eval-jobs nix-fast-build;
 
-      nix-serve-ng = prev.nix-serve-ng.override {
-        inherit nix;
-      };
-    }
-)
+  nullCheck = n: v:
+    if nix == null
+    then prev.${n}
+    else v;
+in
+  mapAttrs nullCheck {
+    inherit nix;
+
+    nix-serve = prev.nix-serve-ng.override {
+      inherit nix;
+    };
+
+    nix-fast-build = nix-fast-build.packages.${final.system}.nix-fast-build.override {
+      nix-eval-jobs =
+        nix-eval-jobs.packages.${final.system}.default.override {
+          inherit nix;
+        }
+        // {
+          inherit nix;
+        };
+    };
+  }