diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/quantity_spec.h
index fb32cc99..d3029c92 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/quantity_spec.h
@@ -109,7 +109,8 @@ struct quantity_spec_interface {
 
   template<typename Self, typename Q>
   [[nodiscard]] constexpr Quantity auto operator()(this Self self, Q&& q) const
-    requires Quantity<std::remove_cvref_t<Q>> && (explicitly_convertible(std::remove_cvref_t<Q>::quantity_spec, self))
+    requires Quantity<std::remove_cvref_t<Q>> &&
+             (explicitly_convertible(std::remove_reference_t<Q>::quantity_spec, self))
   {
     return make_quantity<reference<self, std::remove_cvref_t<Q>::unit>{}>(std::forward<Q>(q).number());
   }
@@ -121,7 +122,8 @@ struct quantity_spec_interface {
   }
 
   template<typename Q>
-    requires Quantity<std::remove_cvref_t<Q>> && (explicitly_convertible(std::remove_cvref_t<Q>::quantity_spec, Self{}))
+    requires Quantity<std::remove_cvref_t<Q>> &&
+             (explicitly_convertible(std::remove_reference_t<Q>::quantity_spec, Self{}))
   [[nodiscard]] constexpr Quantity auto operator()(Q&& q) const
   {
     return make_quantity<reference<Self{}, std::remove_cvref_t<Q>::unit>{}>(std::forward<Q>(q).number());
@@ -296,7 +298,8 @@ struct quantity_spec<Self, QS, Args...> : std::remove_const_t<decltype(QS)> {
   }
 
   template<typename Q>
-    requires Quantity<std::remove_cvref_t<Q>> && (explicitly_convertible(std::remove_cvref_t<Q>::quantity_spec, Self{}))
+    requires Quantity<std::remove_cvref_t<Q>> &&
+             (explicitly_convertible(std::remove_reference_t<Q>::quantity_spec, Self{}))
   [[nodiscard]] constexpr Quantity auto operator()(Q&& q) const
   {
     return make_quantity<reference<Self{}, std::remove_cvref_t<Q>::unit>{}>(std::forward<Q>(q).number());