Index: libcxx/include/cmath
===================================================================
--- libcxx/include/cmath
+++ libcxx/include/cmath
@@ -560,7 +560,7 @@
 
 template <class _A1>
 _LIBCPP_ALWAYS_INLINE
-typename enable_if<is_floating_point<_A1>::value, bool>::type
+_LIBCPP_CONSTEXPR typename enable_if<is_floating_point<_A1>::value, bool>::type
 __libcpp_isnan(_A1 __lcpp_x) _NOEXCEPT
 {
 #if __has_builtin(__builtin_isnan)
@@ -572,7 +572,7 @@
 
 template <class _A1>
 _LIBCPP_ALWAYS_INLINE
-typename enable_if<!is_floating_point<_A1>::value, bool>::type
+_LIBCPP_CONSTEXPR typename enable_if<!is_floating_point<_A1>::value, bool>::type
 __libcpp_isnan(_A1 __lcpp_x) _NOEXCEPT
 {
     return isnan(__lcpp_x);
@@ -580,7 +580,7 @@
 
 template <class _A1>
 _LIBCPP_ALWAYS_INLINE
-typename enable_if<is_floating_point<_A1>::value, bool>::type
+_LIBCPP_CONSTEXPR typename enable_if<is_floating_point<_A1>::value, bool>::type
 __libcpp_isinf(_A1 __lcpp_x) _NOEXCEPT
 {
 #if __has_builtin(__builtin_isinf)
@@ -592,7 +592,7 @@
 
 template <class _A1>
 _LIBCPP_ALWAYS_INLINE
-typename enable_if<!is_floating_point<_A1>::value, bool>::type
+_LIBCPP_CONSTEXPR typename enable_if<!is_floating_point<_A1>::value, bool>::type
 __libcpp_isinf(_A1 __lcpp_x) _NOEXCEPT
 {
     return isinf(__lcpp_x);
@@ -600,7 +600,7 @@
 
 template <class _A1>
 _LIBCPP_ALWAYS_INLINE
-typename enable_if<is_floating_point<_A1>::value, bool>::type
+_LIBCPP_CONSTEXPR typename enable_if<is_floating_point<_A1>::value, bool>::type
 __libcpp_isfinite(_A1 __lcpp_x) _NOEXCEPT
 {
 #if __has_builtin(__builtin_isfinite)
@@ -612,7 +612,7 @@
 
 template <class _A1>
 _LIBCPP_ALWAYS_INLINE
-typename enable_if<!is_floating_point<_A1>::value, bool>::type
+_LIBCPP_CONSTEXPR typename enable_if<!is_floating_point<_A1>::value, bool>::type
 __libcpp_isfinite(_A1 __lcpp_x) _NOEXCEPT
 {
     return isfinite(__lcpp_x);
Index: libcxx/test/libcxx/numerics/c.math/constexpr-fns.pass.cpp
===================================================================
--- /dev/null
+++ libcxx/test/libcxx/numerics/c.math/constexpr-fns.pass.cpp
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// Check that the overloads of std::__libcpp_{isnan,isinf,isfinite} that take
+// floating-point values are evaluatable from constexpr contexts.
+//
+// These functions need to be constexpr in order to be called from CUDA, see
+// https://reviews.llvm.org/D25403.  They don't actually need to be
+// constexpr-evaluatable, but that's what we check here, since we can't check
+// true constexpr-ness.
+
+#include <cmath>
+
+#include "test_macros.h"
+
+#ifndef _LIBCPP_VERSION
+#error _LIBCPP_VERSION not defined
+#endif
+
+#if TEST_STD_VER >= 11
+constexpr bool a = std::__libcpp_isnan(0.);
+constexpr bool b = std::__libcpp_isinf(0.0);
+constexpr bool c = std::__libcpp_isfinite(0.0);
+#endif
+
+int main()
+{
+  return 0;
+}