diff --git a/fn.nix b/fn.nix
index 2633632..3ea5a36 100644
--- a/fn.nix
+++ b/fn.nix
@@ -69,4 +69,11 @@ rec {
           true)
     ))
     ld);
+  makeOptionTypeList = path: (lists.forEach
+    # get a list of all files ending in .nix in path
+    (filter (filePath: hasSuffix ".nix" filePath)
+      (lsfRec path true))
+    # remove leading path and trailing ".nix", replace every slash with "::"
+    (replaceStrings [ "${path}/" "/" ".nix" ] [ "" "::" "" ])
+  );
 }
diff --git a/options/machine.nix b/options/machine.nix
index 1362671..e096c06 100644
--- a/options/machine.nix
+++ b/options/machine.nix
@@ -5,9 +5,8 @@ with lib;
 
 let
   cfg = config.machine;
-  metapkgs = let
-    pPath = (toString ../pkgsets);
-  in (lists.forEach (fn.lsfRec pPath true) (v: replaceStrings [ "${pPath}/" "/" ".nix" ] [ "" "::" "" ] v));
+  pkgsetList = fn.makeOptionTypeList (toString ../pkgsets);
+  serviceList = fn.makeOptionTypeList (toString ../services);
   pkgOption = pname: {
     name = pname;
     value = rec {
@@ -30,16 +29,16 @@ let
 in {
   options.machine = {
     pkgs = mkOption {
-      type = (types.listOf (types.enum metapkgs));
+      type = (types.listOf (types.enum pkgsetList));
       default = [ "base" ];
       description = ''
         The list of metapackages to be installed.
       '';
     };
     # Package names containing '::' are sub packages and should not have their own pkgset.
-    pkgsets = listToAttrs (map pkgOption (lists.filter (v: !(strings.hasInfix "::" v)) metapkgs));
+    pkgsets = listToAttrs (map pkgOption (lists.filter (v: !(strings.hasInfix "::" v)) pkgsetList));
     services = mkOption {
-      type = types.listOf types.str;
+      type = (types.listOf (types.enum serviceList));
       default = [];
       description = ''
         List of services to be enabled.