From a7704d28bd9be57ccc4824bdd3fa70c1c2a8522a Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Fri, 21 Nov 2025 14:16:14 +0100
Subject: [PATCH] Don't change sign of nans

---
 include/boost/decimal/detail/cmath/abs.hpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/boost/decimal/detail/cmath/abs.hpp b/include/boost/decimal/detail/cmath/abs.hpp
index b7da73126..e0fca14c6 100644
--- a/include/boost/decimal/detail/cmath/abs.hpp
+++ b/include/boost/decimal/detail/cmath/abs.hpp
@@ -22,7 +22,14 @@ BOOST_DECIMAL_EXPORT template <typename T>
 constexpr auto abs BOOST_DECIMAL_PREVENT_MACRO_SUBSTITUTION (const T rhs) noexcept
     BOOST_DECIMAL_REQUIRES(detail::is_decimal_floating_point_v, T)
 {
-    return signbit(rhs) ? -rhs : rhs;
+    if (BOOST_DECIMAL_LIKELY(!isnan(rhs)))
+    {
+        return signbit(rhs) ? -rhs : rhs;
+    }
+    else
+    {
+        return issignaling(rhs) ? nan_conversion(rhs) : rhs;
+    }
 }
 
 } // namespace decimal