diff --git a/postfix.nix b/postfix.nix
index 3a1d955..d0da883 100644
--- a/postfix.nix
+++ b/postfix.nix
@@ -6,6 +6,8 @@ let
 
   allDomains = [ cfg.domain ] ++ cfg.local-domains;
 
+  concatMapAttrsToList = f: as: concatLists (mapAttrsToList f as);
+
 in {
   options.fudo.mail.postfix = with types; {
     enable = mkEnableOption "Enable Postfix SMTP server.";
@@ -239,8 +241,6 @@ in {
 
         dnsBlacklists = cfg.dns-blacklists;
 
-        concatMapAttrsToList = f: as: concatLists (mapAttrsToList f as);
-
         mapFiles = let
           writeEntries = filename: entries:
             pkgs.writeText filename (concatStringsSep "\n" entries);