diff --git a/lib/private.nix b/lib/private.nix
index e8605daa..f54b16c0 100644
--- a/lib/private.nix
+++ b/lib/private.nix
@@ -44,6 +44,8 @@ rec {
           ({ inherit key; } // settings))
       secrets;
 
+  isInternal = config: config ? _isInsideFds && config._isInsideFds;
+
   getUsers = type: users:
     let
       userModules = lib.filesToAttr ../users/${type};