diff --git a/flake.nix b/flake.nix
index 843b66a..55d1ad0 100644
--- a/flake.nix
+++ b/flake.nix
@@ -228,9 +228,16 @@
 
       formatter = forEachSystem (system: (mkPkgs system).nixfmt);
 
-      checks = forEachSystem (system: {
-        inherit (self.packages.${system}) cf codex;
-      });
+      checks = forEachSystem (
+        system:
+        let
+          customPkgs = self.packages.${system};
+        in
+        {
+          inherit (customPkgs) cf;
+        }
+        // lib.optionalAttrs (customPkgs ? codex) { inherit (customPkgs) codex; }
+      );
 
       packages = forEachSystem (
         system:
diff --git a/packages/codex.nix b/packages/codex.nix
index 8d38cf4..db037ba 100644
--- a/packages/codex.nix
+++ b/packages/codex.nix
@@ -1,6 +1,11 @@
 { pkgs, llm-agents }:
 let
-  upstream = llm-agents.packages.${pkgs.stdenv.hostPlatform.system}.codex;
+  system = pkgs.stdenv.hostPlatform.system;
+  upstream =
+    if builtins.hasAttr system llm-agents.packages then
+      llm-agents.packages.${system}.codex
+    else
+      throw "codex: llm-agents does not provide packages.${system} (supported: ${builtins.concatStringsSep ", " (builtins.attrNames llm-agents.packages)})";
   manifest = pkgs.writeText "codex-package.json" (
     builtins.toJSON {
       layoutVersion = 1;
diff --git a/packages/default.nix b/packages/default.nix
index 78a16ed..109e621 100644
--- a/packages/default.nix
+++ b/packages/default.nix
@@ -1,6 +1,18 @@
-{ pkgs, llm-agents, ... }:
+{
+  pkgs,
+  lib,
+  llm-agents,
+  ...
+}:
+let
+  # llm-agents does not publish every platform (it dropped x86_64-darwin), so
+  # expose codex only where the input provides it.
+  hasCodex = builtins.hasAttr pkgs.stdenv.hostPlatform.system llm-agents.packages;
+in
 {
   cf = pkgs.callPackage ./cf.nix { };
-  codex = pkgs.callPackage ./codex.nix { inherit llm-agents; };
   pikpak-cli = pkgs.callPackage ./pikpak-cli.nix { };
 }
+// lib.optionalAttrs hasCodex {
+  codex = pkgs.callPackage ./codex.nix { inherit llm-agents; };
+}