diff --git a/src/core/include/mp-units/bits/quantity_cast.h b/src/core/include/mp-units/bits/quantity_cast.h
index c5db82f18..a78bac95e 100644
--- a/src/core/include/mp-units/bits/quantity_cast.h
+++ b/src/core/include/mp-units/bits/quantity_cast.h
@@ -48,7 +48,6 @@ namespace mp_units {
 template<QuantitySpec auto ToQS, typename Q>
   requires Quantity<std::remove_cvref_t<Q>> && (castable(Q::quantity_spec, ToQS))
 [[nodiscard]] constexpr Quantity auto quantity_cast(Q&& q)
-  requires Quantity<std::remove_cvref_t<Q>> && (castable(q.quantity_spec, ToQS))
 {
   if constexpr (detail::QuantityKindSpec<std::remove_const_t<decltype(ToQS)>> &&
                 AssociatedUnit<std::remove_const_t<decltype(Q::unit)>>)