diff --git a/nix/templates/harness-base.nix b/nix/templates/harness-base.nix
index 64a8b02..efb3b37 100644
--- a/nix/templates/harness-base.nix
+++ b/nix/templates/harness-base.nix
@@ -329,8 +329,10 @@
       # expected to set `_module.args.flakeInputs = builtins.removeAttrs inputs ["self"]`.
       # If `self` leaks into flakeInputs the agent gets a spurious attrset
       # entry that can shadow real inputs and is almost certainly a bug.
+      # Guard with `or {}` so standalone evaluation stays clean when
+      # flakeInputs is absent from _module.args.
       {
-        assertion = !(builtins.hasAttr "self" flakeInputs);
+        assertion = !(builtins.hasAttr "self" (config._module.args.flakeInputs or { }));
         message = ''
           hyperhive: `flakeInputs` must not contain "self".
           In your agent flake.nix, use: