diff --git a/nixos/modules/system/boot/loader/grub/grub.nix b/nixos/modules/system/boot/loader/grub/grub.nix
index ee07d8657efd..f1da2f41b5c1 100644
--- a/nixos/modules/system/boot/loader/grub/grub.nix
+++ b/nixos/modules/system/boot/loader/grub/grub.nix
@@ -385,7 +385,7 @@ in
       };
 
       default = mkOption {
-        default = 0;
+        default = "0";
         type = types.str;
         description = ''
           Index of the default menu item to be booted.