diff --git a/src/dotfiles/util.nix b/src/dotfiles/util.nix
index a38ca34..5f87cff 100644
--- a/src/dotfiles/util.nix
+++ b/src/dotfiles/util.nix
@@ -30,12 +30,11 @@ in
   deriveMac =
     name:
     let
-      octet = i: builtins.substring (i * 2) 2 hash;
       hash = builtins.hashString "sha256" name;
     in
     lib.concatStringsSep ":" (
       [ "02" ]
-      ++ map octet [
+      ++ map (i: builtins.substring (i * 2) 2 hash) [
         0
         1
         2