Index: libcxx/include/__compare/ordering.h
===================================================================
--- libcxx/include/__compare/ordering.h
+++ libcxx/include/__compare/ordering.h
@@ -40,8 +40,12 @@
 inline constexpr bool __one_of_v = (is_same_v<_Tp, _Args> || ...);
 
 struct _CmpUnspecifiedParam {
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  _CmpUnspecifiedParam(int _CmpUnspecifiedParam::*) noexcept {}
+  _LIBCPP_HIDE_FROM_ABI consteval
+  _CmpUnspecifiedParam(int __literal_zero) noexcept {
+    if (__literal_zero != 0) {
+      __builtin_abort();
+    }
+  }
 
   template<class _Tp, class = enable_if_t<!__one_of_v<_Tp, int, partial_ordering, weak_ordering, strong_ordering>>>
   _CmpUnspecifiedParam(_Tp) = delete;
Index: libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp
===================================================================
--- libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp
+++ libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// ADDITIONAL_COMPILE_FLAGS: -Wzero-as-null-pointer-constant
 
 // <compare>
 
Index: libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp
===================================================================
--- libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp
+++ libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// ADDITIONAL_COMPILE_FLAGS: -Wzero-as-null-pointer-constant
 
 // <compare>
 
Index: libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp
===================================================================
--- libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp
+++ libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// ADDITIONAL_COMPILE_FLAGS: -Wzero-as-null-pointer-constant
 
 // <compare>