diff --git a/flake.nix b/flake.nix
index ee24c8f13..13ca5e618 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,6 +7,10 @@
   };
 
   inputs = {
+    # Ensure Nix fetches git submodules (vendor/*) when evaluating this flake.
+    # Requires Nix >= 2.27.  Consumers no longer need '?submodules=1' in the URL.
+    self.submodules = true;
+
     # We are pinning the commit because ultimately we want to use same commit across different projects.
     # A commit from nixpkgs 24.11 release : https://github.com/NixOS/nixpkgs/tree/release-24.11
     nixpkgs.url = "github:NixOS/nixpkgs/0ef228213045d2cdb5a169a95d63ded38670b293";
diff --git a/nix/default.nix b/nix/default.nix
index 7df58df60..816d0aed8 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -12,7 +12,7 @@
   zerokitRln,
 }:
 
-assert pkgs.lib.assertMsg ((src.submodules or true) == true)
+assert pkgs.lib.assertMsg (builtins.pathExists "${src}/vendor/nimbus-build-system/scripts")
   "Unable to build without submodules. Append '?submodules=1#' to the URI.";
 
 let