diff --git a/nixos/modules/virtualisation/virtualbox-image.nix b/nixos/modules/virtualisation/virtualbox-image.nix
index 71bdf31a98d2..06bea2d8acff 100644
--- a/nixos/modules/virtualisation/virtualbox-image.nix
+++ b/nixos/modules/virtualisation/virtualbox-image.nix
@@ -111,5 +111,5 @@ with pkgs.lib;
   # Prevent logging in as root without a password.  For NixOps, we
   # don't need this because the user can login via SSH, and for the
   # demo images, there is a demo user account that can sudo to root.
-  security.initialRootPassword = "!";
+  security.initialRootPassword = mkDefault "!";
 }