From 4fb1bc4f359c2fcec384fd32da89ac45f0bf2723 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Mon, 29 Dec 2025 18:24:17 +0100
Subject: [PATCH] refactor: `quantity_cast` constraints improved

---
 src/core/include/mp-units/framework/quantity_cast.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/core/include/mp-units/framework/quantity_cast.h b/src/core/include/mp-units/framework/quantity_cast.h
index 018317eb1..276073e55 100644
--- a/src/core/include/mp-units/framework/quantity_cast.h
+++ b/src/core/include/mp-units/framework/quantity_cast.h
@@ -58,7 +58,8 @@ namespace mp_units {
  * @tparam ToQS a quantity specification to use for a target quantity
  */
 template<QuantitySpec auto ToQS, typename FwdQ, Quantity Q = std::remove_cvref_t<FwdQ>>
-  requires(castable(Q::quantity_spec, ToQS)) && (MP_UNITS_WEAK_UNIT_OF(MP_UNITS_NONCONST_TYPE(Q::unit), ToQS))
+  requires(castable(Q::quantity_spec, ToQS)) &&
+          requires { typename quantity<make_reference(ToQS, Q::unit), typename Q::rep>; }
 [[nodiscard]] constexpr Quantity auto quantity_cast(FwdQ&& q)
 {
   return quantity{std::forward<FwdQ>(q).numerical_value_is_an_implementation_detail_, make_reference(ToQS, Q::unit)};