Index: libcxx/include/__compare/ordering.h
===================================================================
--- libcxx/include/__compare/ordering.h
+++ libcxx/include/__compare/ordering.h
@@ -39,9 +39,15 @@
 template<class _Tp, class... _Args>
 inline constexpr bool __one_of_v = (is_same_v<_Tp, _Args> || ...);
 
+void __literal_zero_is_expected();
+
 struct _CmpUnspecifiedParam {
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  _CmpUnspecifiedParam(int _CmpUnspecifiedParam::*) noexcept {}
+  consteval
+  _CmpUnspecifiedParam(int __literal_zero) noexcept {
+    if (__literal_zero != 0) {
+      __literal_zero_is_expected();
+    }
+  }
 
   template<class _Tp, class = enable_if_t<!__one_of_v<_Tp, int, partial_ordering, weak_ordering, strong_ordering>>>
   _CmpUnspecifiedParam(_Tp) = delete;
Index: libcxx/test/libcxx/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp
===================================================================
--- libcxx/test/libcxx/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp
+++ libcxx/test/libcxx/language.support/cmp/cmp.categories.pre/zero_type.verify.cpp
@@ -8,10 +8,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 
-// In MSVC mode, there's a slightly different number of errors printed for
-// each of these, so it doesn't add up to the exact expected count of 18.
-// XFAIL: msvc
-
 // <compare>
 
 // Ensure we reject all cases where an argument other than a literal 0 is used
@@ -23,9 +19,7 @@
   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)
+  void(nullptr op v)
 
 #define TEST_PASS(v, op)                                                       \
   void(v op 0);                                                                \
@@ -33,13 +27,13 @@
 
 template <typename T>
 void test_category(T v) {
-  TEST_FAIL(v, ==);  // expected-error 18 {{}}
-  TEST_FAIL(v, !=);  // expected-error 18 {{}}
-  TEST_FAIL(v, <);   // expected-error 18 {{}}
-  TEST_FAIL(v, <=);  // expected-error 18 {{}}
-  TEST_FAIL(v, >);   // expected-error 18 {{}}
-  TEST_FAIL(v, >=);  // expected-error 18 {{}}
-  TEST_FAIL(v, <=>); // expected-error 18 {{}}
+  TEST_FAIL(v, ==);  // expected-error 12 {{}}
+  TEST_FAIL(v, !=);  // expected-error 12 {{}}
+  TEST_FAIL(v, <);   // expected-error 12 {{}}
+  TEST_FAIL(v, <=);  // expected-error 12 {{}}
+  TEST_FAIL(v, >);   // expected-error 12 {{}}
+  TEST_FAIL(v, >=);  // expected-error 12 {{}}
+  TEST_FAIL(v, <=>); // expected-error 12 {{}}
 
   TEST_PASS(v, ==);
   TEST_PASS(v, !=);
Index: libcxx/test/support/controlled_allocators.h
===================================================================
--- libcxx/test/support/controlled_allocators.h
+++ libcxx/test/support/controlled_allocators.h
@@ -72,7 +72,7 @@
 
     std::size_t last_size = 0;
     std::size_t last_align = 0;
-    void * last_pointer = 0;
+    void * last_pointer = nullptr;
 
     std::size_t last_alloc_size = 0;
     std::size_t last_alloc_align = 0;
Index: libcxx/utils/libcxx/test/dsl.py
===================================================================
--- libcxx/utils/libcxx/test/dsl.py
+++ libcxx/utils/libcxx/test/dsl.py
@@ -253,7 +253,7 @@
       #include <locale.h>
       int main(int argc, char** argv) {
         for (int i = 1; i < argc; i++) {
-          if (::setlocale(LC_ALL, argv[i]) != NULL) {
+          if (::setlocale(LC_ALL, argv[i]) != nullptr) {
             return 0;
           }
         }
Index: libcxx/utils/libcxx/test/params.py
===================================================================
--- libcxx/utils/libcxx/test/params.py
+++ libcxx/utils/libcxx/test/params.py
@@ -18,6 +18,7 @@
   '-Wshadow',
   '-Wundef',
   '-Wunused-template',
+  '-Wzero-as-null-pointer-constant',
   '-Wno-unused-command-line-argument',
   '-Wno-attributes',
   '-Wno-pessimizing-move',