diff --git a/codex-rs/core/tests/common/test_codex.rs b/codex-rs/core/tests/common/test_codex.rs
index 7bd5763d19..9776291dd7 100644
--- a/codex-rs/core/tests/common/test_codex.rs
+++ b/codex-rs/core/tests/common/test_codex.rs
@@ -186,6 +186,7 @@ impl TestCodexBuilder {
                 SessionSource::Exec,
                 Some(model_catalog),
                 CollaborationModesConfig::default(),
+                config.plan_mode_developer_instructions.clone(),
             )
         } else {
             codex_core::test_support::thread_manager_with_models_provider_and_home(