diff --git a/nixos/modules/services/networking/freenet.nix b/nixos/modules/services/networking/freenet.nix
index a0c67796377b..c95eb5d271af 100644
--- a/nixos/modules/services/networking/freenet.nix
+++ b/nixos/modules/services/networking/freenet.nix
@@ -15,7 +15,7 @@ in
       enable = lib.mkEnableOption "Freenet daemon";
 
       nice = lib.mkOption {
-        type = lib.types.int;
+        type = lib.types.ints.between (-20) 19;
         default = 10;
         description = "Set the nice level for the Freenet daemon";
       };