diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/quantity_spec.h
index 632ff81c..83d13f67 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/quantity_spec.h
@@ -104,7 +104,10 @@ struct quantity_spec_interface {
   template<typename Self, UnitOf<Self{}> U>
   [[nodiscard]] consteval Reference auto operator[](this Self self, U u)
   {
-    return reference<self, u>{};
+    if constexpr (detail::QuantityKindSpec<Self>)
+      return u;
+    else
+      return reference<self, u>{};
   }
 
   template<typename Self, typename Q>
@@ -118,7 +121,10 @@ struct quantity_spec_interface {
   template<typename Self_ = Self, UnitOf<Self_{}> U>
   [[nodiscard]] consteval Reference auto operator[](U u) const
   {
-    return reference<Self{}, u>{};
+    if constexpr (detail::QuantityKindSpec<Self_>)
+      return u;
+    else
+      return reference<Self{}, u>{};
   }
 
   template<typename Q, typename Self_ = Self>
@@ -294,7 +300,10 @@ struct quantity_spec<Self, QS, Args...> : std::remove_const_t<decltype(QS)> {
   template<typename Self_ = Self, UnitOf<Self_{}> U>
   [[nodiscard]] consteval Reference auto operator[](U u) const
   {
-    return reference<Self{}, u>{};
+    if constexpr (detail::QuantityKindSpec<Self>)
+      return u;
+    else
+      return reference<Self{}, u>{};
   }
 
   template<typename Q, typename Self_ = Self>
diff --git a/test/unit_test/static/reference_test.cpp b/test/unit_test/static/reference_test.cpp
index 83e2cc60..7ab7de56 100644
--- a/test/unit_test/static/reference_test.cpp
+++ b/test/unit_test/static/reference_test.cpp
@@ -105,6 +105,13 @@ inline constexpr struct kilometre_ : decltype(si::kilo<metre>) {} kilometre;
 inline constexpr struct bit_ : named_unit<"bit", one, kind_of<storage_capacity>> {} bit;
 // clang-format on
 
+
+static_assert(is_of_type<length[metre], reference<length, metre>>);
+static_assert(is_of_type<kind_of<length>[metre], metre_>);
+
+static_assert(is_of_type<(length / time)[metre / second], reference<length / time, metre / second>>);
+static_assert(is_of_type<(kind_of<length> / kind_of<time>)[metre / second], derived_unit<metre_, per<second_>>>);
+
 // Unit as a reference
 static_assert(is_of_type<42 * metre, quantity<metre, int>>);
 static_assert(quantity<metre, int>::quantity_spec == length);