diff --git a/nixos/modules/services/networking/mailpile.nix b/nixos/modules/services/networking/mailpile.nix
index b79ee11d17db..4673a2580b60 100644
--- a/nixos/modules/services/networking/mailpile.nix
+++ b/nixos/modules/services/networking/mailpile.nix
@@ -21,11 +21,13 @@ in
       enable = mkEnableOption "Mailpile the mail client";
 
       hostname = mkOption {
+        type = types.str;
         default = "localhost";
         description = "Listen to this hostname or ip.";
       };
       port = mkOption {
-        default = "33411";
+        type = types.port;
+        default = 33411;
         description = "Listen on this port.";
       };
     };