Index: test/support/poisoned_hash_helper.hpp
===================================================================
--- test/support/poisoned_hash_helper.hpp
+++ test/support/poisoned_hash_helper.hpp
@@ -14,6 +14,7 @@
 #include <cassert>
 
 #include "test_macros.h"
+#include "test_workarounds.h"
 
 #if TEST_STD_VER < 11
 #error this header may only be used in C++11 or newer
@@ -49,9 +50,11 @@
 // specializations of hash for nullptr t and all cv-unqualified
 // arithmetic, enumeration, and pointer types.
 using LibraryHashTypes = TypeList<
+#if !defined(TEST_WORKAROUND_C1XX_BROKEN_NULLPTR_CONVERSION_OPERATOR)
 #if TEST_STD_VER > 14
       decltype(nullptr),
 #endif
+#endif
       bool,
       char,
       signed char,
Index: test/support/test.workarounds/c1xx_broken_nullptr_conversion_operator.pass.cpp
===================================================================
--- /dev/null
+++ test/support/test.workarounds/c1xx_broken_nullptr_conversion_operator.pass.cpp
@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// Verify TEST_WORKAROUND_C1XX_BROKEN_NULLPTR_CONVERSION_OPERATOR.
+
+#include "test_workarounds.h"
+
+#include <type_traits>
+
+struct ConvertsToNullptr {
+  using DestType = decltype(nullptr);
+  operator DestType() const { return nullptr; }
+};
+
+int main() {
+#if defined(TEST_WORKAROUND_C1XX_BROKEN_NULLPTR_CONVERSION_OPERATOR)
+  static_assert(!std::is_convertible<ConvertsToNullptr, decltype(nullptr)>::value, "");
+#else
+  static_assert(std::is_convertible<ConvertsToNullptr, decltype(nullptr)>::value, "");
+#endif
+}
Index: test/support/test_macros.h
===================================================================
--- test/support/test_macros.h
+++ test/support/test_macros.h
@@ -52,6 +52,17 @@
 #define TEST_HAS_BUILTIN_IDENTIFIER(X) 0
 #endif
 
+#if defined(__clang__)
+#define TEST_COMPILER_CLANG
+# if defined(__apple_build_version__)
+#   define TEST_COMPILER_APPLE_CLANG
+# endif
+#elif defined(_MSC_VER)
+# define TEST_COMPILER_C1XX
+#elif defined(__GNUC__)
+# define TEST_COMPILER_GCC
+#endif
+
 #if defined(__apple_build_version__)
 #define TEST_APPLE_CLANG_VER (__clang_major__ * 100) + __clang_minor__
 #elif defined(__clang_major__)
Index: test/support/test_workarounds.h
===================================================================
--- /dev/null
+++ test/support/test_workarounds.h
@@ -0,0 +1,20 @@
+// -*- C++ -*-
+//===---------------------------- test_macros.h ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SUPPORT_TEST_WORKAROUNDS_H
+#define SUPPORT_TEST_WORKAROUNDS_H
+
+#include "test_macros.h"
+
+#if defined(TEST_COMPILER_C1XX)
+# define TEST_WORKAROUND_C1XX_BROKEN_NULLPTR_CONVERSION_OPERATOR
+#endif
+
+#endif // SUPPORT_TEST_WORKAROUNDS_H