diff --git a/cmake/warnings.cmake b/cmake/warnings.cmake
index cf1a8435..a4283dde 100644
--- a/cmake/warnings.cmake
+++ b/cmake/warnings.cmake
@@ -73,6 +73,11 @@ macro(_set_flags)
 
     set(GCC_WARNINGS
             ${CLANG_WARNINGS}
+            -Wno-float-conversion
+            -Wno-shorten-64-to-32
+            -Wno-implicit-float-conversion
+            -Wno-implicit-int-float-conversion
+            -Wno-implicit-int-conversion
             -Wmisleading-indentation # warn if indentation implies blocks where blocks do not exist
             -Wduplicated-cond # warn if if / else chain has duplicated conditions
             -Wduplicated-branches # warn if if / else branches have duplicated code
diff --git a/src/include/units/bits/external/hacks.h b/src/include/units/bits/external/hacks.h
index adae44f2..e9fec31f 100644
--- a/src/include/units/bits/external/hacks.h
+++ b/src/include/units/bits/external/hacks.h
@@ -31,7 +31,11 @@
 #define COMP_MSVC _MSC_VER
 #endif
 
-#if COMP_CLANG && false
+#if defined(COMP_CLANG) && !defined(UNITS_LIBCXX)
+#define UNITS_LIBCXX 0
+#endif
+
+#if COMP_CLANG && UNITS_LIBCXX
 
 #include <concepts/compare.hpp>
 #include <concepts/concepts.hpp>
@@ -60,7 +64,7 @@ namespace std {
 template<class T>
 concept default_constructible = constructible_from<T>;
 
-#elif COMP_CLANG && false
+#elif COMP_CLANG && UNITS_LIBCXX
 
 // concepts
 using concepts::three_way_comparable;
diff --git a/src/include/units/quantity_cast.h b/src/include/units/quantity_cast.h
index 73702716..d8bc39e5 100644
--- a/src/include/units/quantity_cast.h
+++ b/src/include/units/quantity_cast.h
@@ -290,7 +290,7 @@ template<typename CastSpec, typename K, typename U, typename Rep>
   requires requires { requires is_specialization_of<CastSpec, quantity_kind>;
               requires requires { quantity_cast<typename CastSpec::quantity_type>(qk.common()); }; } ||
            requires { requires Kind<CastSpec>; requires UnitOf<U, typename CastSpec::dimension>; } ||
-           requires { requires requires { quantity_cast<CastSpec>(qk.common()); }; }
+           requires { quantity_cast<CastSpec>(qk.common()); }
 {
   if constexpr (is_specialization_of<CastSpec, quantity_kind>)
     return CastSpec(quantity_cast<typename CastSpec::quantity_type>(qk.common()));
@@ -349,7 +349,7 @@ template<typename CastSpec, typename PK, typename U, typename Rep>
   requires requires { requires is_specialization_of<CastSpec, quantity_point_kind>;
               requires requires { quantity_kind_cast<typename CastSpec::quantity_kind_type>(qpk.relative()); }; } ||
            requires { requires PointKind<CastSpec> && UnitOf<U, typename CastSpec::dimension>; } ||
-           requires { requires requires { quantity_kind_cast<CastSpec>(qpk.relative()); }; }
+           requires { quantity_kind_cast<CastSpec>(qpk.relative()); }
 {
   if constexpr (is_specialization_of<CastSpec, quantity_point_kind>)
     return CastSpec(quantity_kind_cast<typename CastSpec::quantity_kind_type>(qpk.relative()));
diff --git a/test/unit_test/static/quantity_test.cpp b/test/unit_test/static/quantity_test.cpp
index 90fa46cc..6d945ec8 100644
--- a/test/unit_test/static/quantity_test.cpp
+++ b/test/unit_test/static/quantity_test.cpp
@@ -44,11 +44,6 @@ using namespace unit_constants;
 
 constexpr auto cgs_cm = cgs::unit_constants::cm;
 
-#if UNITS_DOWNCAST_MODE == 0
-template<typename T, typename U>
-constexpr bool is_same_v = equivalent<T, U>;
-#endif
-
 
 //////////////////////////////
 // quantity class invariants
@@ -748,7 +743,7 @@ static_assert(quantity_cast<dim_speed, kilometre_per_hour>(2000.0_q_m / 3600.0_q
 static_assert(quantity_cast<dim_length>(1 * cgs_cm) == 1 * cm);
 
 static_assert(is_same_v<decltype(quantity_cast<litre>(2_q_dm3)), volume<litre, std::int64_t>>);
-static_assert(!std::same_as<decltype(quantity_cast<litre>(2_q_dm3)), volume<cubic_decimetre, std::int64_t>>);
+static_assert(!is_same_v<decltype(quantity_cast<litre>(2_q_dm3)), volume<cubic_decimetre, std::int64_t>>);
 
 ////////////////
 // downcasting