diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -847,6 +847,12 @@
 #  define _LIBCPP_CONSTEXPR constexpr
 #endif
 
+#ifndef __cpp_consteval
+#  define _LIBCPP_CONSTEVAL _LIBCPP_CONSTEXPR
+#else
+#  define _LIBCPP_CONSTEVAL consteval
+#endif
+
 #ifdef _LIBCPP_CXX03_LANG
 #  define _LIBCPP_DEFAULT {}
 #else
diff --git a/libcxx/include/compare b/libcxx/include/compare
--- a/libcxx/include/compare
+++ b/libcxx/include/compare
@@ -154,8 +154,13 @@
   __unordered = -127
 };
 
-struct _CmpUnspecifiedType;
-using _CmpUnspecifiedParam = void (_CmpUnspecifiedType::*)();
+struct _CmpUnspecifiedParam {
+  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEVAL
+  _CmpUnspecifiedParam(int _CmpUnspecifiedParam::*) {}
+
+  template<typename _Tp, typename = _VSTD::enable_if_t<!_VSTD::is_same_v<_Tp, int>>>
+  _CmpUnspecifiedParam(_Tp) = delete;
+};
 
 class  weak_equality {
   _LIBCPP_INLINE_VISIBILITY
diff --git a/libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.fail.cpp b/libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.fail.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/language.support/cmp/cmp.categories.pre/zero_type.fail.cpp
@@ -0,0 +1,43 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <compare>
+
+// Ensure we reject all cases where an argument other than a literal 0 is used
+// for a comparison against a comparison category type.
+
+#include <compare>
+
+#define TEST_OP(op)                                                            \
+  void(v op 0L);                                                               \
+  void(0L op v);                                                               \
+  void(v op nullptr);                                                          \
+  void(nullptr op v);                                                          \
+  void(v op(1 - 1));                                                           \
+  void((1 - 1) op v);
+
+template <typename T>
+void test_category(T v) {
+  TEST_OP(==);  // expected-error 18 {{}}
+  TEST_OP(!=);  // expected-error 18 {{}}
+  TEST_OP(<);   // expected-error 18 {{}}
+  TEST_OP(<=);  // expected-error 18 {{}}
+  TEST_OP(>);   // expected-error 18 {{}}
+  TEST_OP(>=);  // expected-error 18 {{}}
+  TEST_OP(<=>); // expected-error 18 {{}}
+}
+
+int main(int, char**) {
+  test_category(std::strong_ordering::equivalent);
+  test_category(std::weak_ordering::equivalent);
+  test_category(std::partial_ordering::equivalent);
+  return 0;
+}