diff --git a/module.nix b/module.nix
index 4c80b9e..6f34c0b 100644
--- a/module.nix
+++ b/module.nix
@@ -6,7 +6,10 @@ in
   options = {
     services.thekenlicht-daemon = {
       enable = lib.mkEnableOption "Enable Module";
-      serialPort = lib.mkStringOption "Serial Port";
+      serialPort = lib.mkOption {
+        name = "Serial Port";
+        type = lib.types.uniq lib.types.str;
+      };
     };
   };