diff --git a/src/core/include/mp-units/bits/external/type_name.h b/src/core/include/mp-units/bits/external/type_name.h
index d4867033..24bdc8a6 100644
--- a/src/core/include/mp-units/bits/external/type_name.h
+++ b/src/core/include/mp-units/bits/external/type_name.h
@@ -6,6 +6,8 @@
 #include <string_view>
 #endif
 
+namespace mp_units::detail {
+
 template<typename T>
 [[nodiscard]] consteval std::string_view type_name()
 {
@@ -40,3 +42,5 @@ template<typename T1, typename T2>
   else
     return v2;
 }
+
+}  // namespace mp_units::detail
diff --git a/src/core/include/mp-units/bits/magnitude.h b/src/core/include/mp-units/bits/magnitude.h
index 3b0f7648..cc9bef1d 100644
--- a/src/core/include/mp-units/bits/magnitude.h
+++ b/src/core/include/mp-units/bits/magnitude.h
@@ -594,7 +594,7 @@ consteval bool less(MagnitudeSpec auto lhs, MagnitudeSpec auto rhs)
   using rhs_base_t = decltype(get_base_value(rhs));
 
   if constexpr (is_named_magnitude<lhs_base_t> && is_named_magnitude<rhs_base_t>)
-    return type_name<lhs_base_t>() < type_name<rhs_base_t>();
+    return detail::type_name<lhs_base_t>() < detail::type_name<rhs_base_t>();
   else if constexpr (!is_named_magnitude<lhs_base_t> && !is_named_magnitude<rhs_base_t>)
     return get_base_value(lhs) < get_base_value(rhs);
   else
diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/quantity_spec.h
index 3679b19e..8539cf5f 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/quantity_spec.h
@@ -96,7 +96,7 @@ template<auto... Args>
 }
 
 template<NamedQuantitySpec Lhs, NamedQuantitySpec Rhs>
-struct quantity_spec_less : std::bool_constant<type_name<Lhs>() < type_name<Rhs>()> {};
+struct quantity_spec_less : std::bool_constant<detail::type_name<Lhs>() < detail::type_name<Rhs>()> {};
 
 template<typename T1, typename T2>
 using type_list_of_quantity_spec_less = expr_less<T1, T2, quantity_spec_less>;
@@ -639,7 +639,7 @@ template<Dimension D1, Dimension D2>
   else if constexpr (rhs == dimension_one)
     return true;
   else
-    return type_name<D1>() < type_name<D2>();
+    return detail::type_name<D1>() < detail::type_name<D2>();
 }
 
 template<QuantitySpec Lhs, QuantitySpec Rhs, bool lhs_eq = requires { Lhs::_equation_; },
@@ -649,7 +649,7 @@ struct ingredients_less :
     std::bool_constant<(lhs_compl > rhs_compl) ||
                        (lhs_compl == rhs_compl && ingredients_dimension_less(Lhs::dimension, Rhs::dimension)) ||
                        (lhs_compl == rhs_compl && Lhs::dimension == Rhs::dimension &&
-                        type_name<Lhs>() < type_name<Rhs>())> {};
+                        detail::type_name<Lhs>() < detail::type_name<Rhs>())> {};
 
 template<typename T1, typename T2>
 using type_list_of_ingredients_less = expr_less<T1, T2, ingredients_less>;
diff --git a/src/core/include/mp-units/unit.h b/src/core/include/mp-units/unit.h
index 5c9fdf9a..abca45ac 100644
--- a/src/core/include/mp-units/unit.h
+++ b/src/core/include/mp-units/unit.h
@@ -644,7 +644,7 @@ template<Unit U1, Unit U2>
       return u2;
     else
       // TODO Check if there is a better choice here
-      return better_type_name(u1, u2);
+      return detail::better_type_name(u1, u2);
   } else {
     constexpr auto canonical_lhs = get_canonical_unit(U1{});
     constexpr auto canonical_rhs = get_canonical_unit(U2{});