diff --git a/variables-module.nix b/variables-module.nix
index 6524e23..e69673f 100644
--- a/variables-module.nix
+++ b/variables-module.nix
@@ -142,6 +142,7 @@ in
           Root SSH Keys
         '';
         type = types.nullOr (types.listOf types.str);
+        default = [];
       };
       passwordAuthentication = mkOption {
         description = ''