diff --git a/include/pybind11/detail/smart_holder_poc.h b/include/pybind11/detail/smart_holder_poc.h
index 1db16b6d6..99aedc9ad 100644
--- a/include/pybind11/detail/smart_holder_poc.h
+++ b/include/pybind11/detail/smart_holder_poc.h
@@ -138,7 +138,8 @@ inline bool is_std_default_delete(const std::type_info &rtti_deleter) {
            || rtti_deleter == typeid(std::default_delete<T const>);
 }
 
-#if !defined(NDEBUG) || true // BAKEIN_WIP: Stress test.
+// Meant to help detecting invalid `reinterpret_cast`s or similar.
+#ifdef PYBIND11_SMART_HOLDER_PADDING_ON
 #    define PYBIND11_SMART_HOLDER_PADDING(N) int PADDING_##N##_[11]
 #else
 #    define PYBIND11_SMART_HOLDER_PADDING(N)