diff --git a/modules/system/activation/top-level.nix b/modules/system/activation/top-level.nix
index 35b6d0bff0c9..118a5c6266e3 100644
--- a/modules/system/activation/top-level.nix
+++ b/modules/system/activation/top-level.nix
@@ -37,6 +37,7 @@ let
 
     system.boot.loader.kernelFile = mkOption {
       default = pkgs.stdenv.platform.kernelTarget;
+      type = types.uniq types.string;
       description = ''
         Name of the kernel file to be passed to the bootloader.
       '';