diff --git a/nixos/modules/services/mail/postfix.nix b/nixos/modules/services/mail/postfix.nix
index ab6ad390600..6c5d7e92702 100644
--- a/nixos/modules/services/mail/postfix.nix
+++ b/nixos/modules/services/mail/postfix.nix
@@ -300,7 +300,7 @@ in
       };
 
       extraConfig = mkOption {
-        type = types.str;
+        type = types.lines;
         default = "";
         description = "
           Extra lines to be added verbatim to the main.cf configuration file.