diff --git a/src/core/include/mp-units/framework/quantity_spec.h b/src/core/include/mp-units/framework/quantity_spec.h
index 3ca46da2..6226cdde 100644
--- a/src/core/include/mp-units/framework/quantity_spec.h
+++ b/src/core/include/mp-units/framework/quantity_spec.h
@@ -508,7 +508,7 @@ template<QuantitySpec Q>
 }  // namespace detail
 
 template<typename Q>
-  requires(!detail::QuantityKindSpec<Q>) && detail::SameQuantitySpec<detail::get_kind_tree_root(Q{}), Q{}>
+  requires(!detail::QuantityKindSpec<Q>) && (detail::get_kind_tree_root(Q{}) == Q{})
 #if MP_UNITS_API_NO_CRTP
 struct kind_of_<Q> final : Q::_base_type_ {
 #else
diff --git a/src/core/include/mp-units/framework/quantity_spec_concepts.h b/src/core/include/mp-units/framework/quantity_spec_concepts.h
index d59229bc..02caaa47 100644
--- a/src/core/include/mp-units/framework/quantity_spec_concepts.h
+++ b/src/core/include/mp-units/framework/quantity_spec_concepts.h
@@ -105,10 +105,6 @@ MP_UNITS_EXPORT template<QuantitySpec Q>
 
 namespace detail {
 
-template<auto QS1, auto QS2>
-concept SameQuantitySpec = QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(QS1))> &&
-                           QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(QS2))> && (QS1 == QS2);
-
 template<QuantitySpec Child, QuantitySpec Parent>
 [[nodiscard]] consteval bool is_child_of(Child ch, Parent p);
 
@@ -118,7 +114,7 @@ concept ChildQuantitySpecOf = (is_child_of(Child, Parent));
 template<auto To, auto From>
 concept NestedQuantityKindSpecOf =
   QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(From))> && QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(To))> &&
-  (!SameQuantitySpec<get_kind(From), get_kind(To)>) && ChildQuantitySpecOf<To, get_kind(From)._quantity_spec_>;
+  (get_kind(From) != get_kind(To)) && ChildQuantitySpecOf<To, get_kind(From)._quantity_spec_>;
 
 template<auto From, auto To>
 concept QuantitySpecConvertibleTo =
diff --git a/src/core/include/mp-units/framework/unit_concepts.h b/src/core/include/mp-units/framework/unit_concepts.h
index 08984c48..b9c96866 100644
--- a/src/core/include/mp-units/framework/unit_concepts.h
+++ b/src/core/include/mp-units/framework/unit_concepts.h
@@ -104,11 +104,11 @@ concept AssociatedUnit = Unit<U> && detail::has_associated_quantity(U{});
  * the provided quantity_spec type.
  */
 MP_UNITS_EXPORT template<typename U, auto QS>
-concept UnitOf = AssociatedUnit<U> && QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(QS))> &&
-                 detail::QuantitySpecConvertibleTo<get_quantity_spec(U{}), QS> &&
-                 // the below is to make `dimensionless[radian]` invalid
-                 (detail::SameQuantitySpec<get_kind(QS), get_kind(get_quantity_spec(U{}))> ||
-                  !detail::NestedQuantityKindSpecOf<get_quantity_spec(U{}), QS>);
+concept UnitOf =
+  AssociatedUnit<U> && QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(QS))> &&
+  detail::QuantitySpecConvertibleTo<get_quantity_spec(U{}), QS> &&
+  // the below is to make `dimensionless[radian]` invalid
+  (get_kind(QS) == get_kind(get_quantity_spec(U{})) || !detail::NestedQuantityKindSpecOf<get_quantity_spec(U{}), QS>);
 
 MP_UNITS_EXPORT template<Unit From, Unit To>
 [[nodiscard]] consteval bool convertible(From from, To to);