--- boost/atomic/detail/float_sizes.hpp.orig	2019-04-10 05:35:21.000000000 +1000
+++ boost/atomic/detail/float_sizes.hpp	2020-10-20 21:52:20.000000000 +1100
@@ -104,6 +104,20 @@
 
 #endif
 
+#if !defined(__clang__) && defined(__GNUC__) && \
+   ((__GNUC__ * 100 + __GNUC_MINOR__) < 490) && \
+   (defined(__BSDSUniX__) || defined(__FreeBSD__))
+# ifndef BOOST_ATOMIC_DETAIL_SIZEOF_FLOAT_VALUE
+#  define BOOST_ATOMIC_DETAIL_SIZEOF_FLOAT_VALUE 4
+# endif
+# ifndef BOOST_ATOMIC_DETAIL_SIZEOF_DOUBLE_VALUE
+#  define BOOST_ATOMIC_DETAIL_SIZEOF_DOUBLE_VALUE 8
+# endif
+# ifndef BOOST_ATOMIC_DETAIL_SIZEOF_LONG_DOUBLE_VALUE
+#  define BOOST_ATOMIC_DETAIL_SIZEOF_LONG_DOUBLE_VALUE 10
+# endif
+#endif
+
 // GCC and compatible compilers define internal macros with builtin type traits
 #if defined(__SIZEOF_FLOAT__)
 #define BOOST_ATOMIC_DETAIL_SIZEOF_FLOAT __SIZEOF_FLOAT__