From fb5641a80a826d73bb73e51d93a1e0742ae3598f Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 8 Sep 2025 13:25:33 +0200
Subject: [PATCH] Fix SFINAE for 2-arg + policy and 3 arg w/o policy

---
 include/boost/math/special_functions/hypot.hpp    | 5 +++--
 include/boost/math/special_functions/math_fwd.hpp | 4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/boost/math/special_functions/hypot.hpp b/include/boost/math/special_functions/hypot.hpp
index d7319de58..c06dfa4c0 100644
--- a/include/boost/math/special_functions/hypot.hpp
+++ b/include/boost/math/special_functions/hypot.hpp
@@ -17,6 +17,7 @@
 #include <boost/math/policies/error_handling.hpp>
 #include <boost/math/special_functions/math_fwd.hpp>
 #include <boost/math/tools/utility.hpp>
+#include <boost/math/tools/numeric_limits.hpp>
 
 namespace boost{ namespace math{ namespace detail{
 
@@ -101,7 +102,7 @@ BOOST_MATH_GPU_ENABLED inline typename tools::promote_args<T1, T2>::type
       static_cast<result_type>(x), static_cast<result_type>(y), policies::policy<>());
 }
 
-template <class T1, class T2, class Policy>
+template <class T1, class T2, class Policy, boost::math::enable_if_t<!boost::math::numeric_limits<Policy>::is_specialized, bool>>
 BOOST_MATH_GPU_ENABLED inline typename tools::promote_args<T1, T2>::type
    hypot(T1 x, T2 y, const Policy& pol)
 {
@@ -110,7 +111,7 @@ BOOST_MATH_GPU_ENABLED inline typename tools::promote_args<T1, T2>::type
       static_cast<result_type>(x), static_cast<result_type>(y), pol);
 }
 
-template <class T1, class T2, class T3, boost::math::enable_if_t<!policies::is_policy<T3>::value, bool> = true>
+template <class T1, class T2, class T3, boost::math::enable_if_t<boost::math::numeric_limits<T3>::is_specialized, bool>>
 BOOST_MATH_GPU_ENABLED tools::promote_args_t<T1, T2, T3>
    hypot(T1 x, T2 y, T3 z)
 {
diff --git a/include/boost/math/special_functions/math_fwd.hpp b/include/boost/math/special_functions/math_fwd.hpp
index a79718f25..8d580b592 100644
--- a/include/boost/math/special_functions/math_fwd.hpp
+++ b/include/boost/math/special_functions/math_fwd.hpp
@@ -636,11 +636,11 @@ namespace boost
    BOOST_MATH_GPU_ENABLED tools::promote_args_t<T1, T2>
          hypot(T1 x, T2 y);
 
-   template <class T1, class T2, class Policy>
+   template <class T1, class T2, class Policy, boost::math::enable_if_t<!boost::math::numeric_limits<Policy>::is_specialized, bool> = true>
    BOOST_MATH_GPU_ENABLED tools::promote_args_t<T1, T2>
          hypot(T1 x, T2 y, const Policy&);
 
-   template <class T1, class T2, class T3, boost::math::enable_if_t<!policies::is_policy<T3>::value, bool> = true>
+   template <class T1, class T2, class T3, boost::math::enable_if_t<boost::math::numeric_limits<T3>::is_specialized, bool> = true>
    BOOST_MATH_GPU_ENABLED tools::promote_args_t<T1, T2, T3>
       hypot(T1 x, T2 y, T3 z);