diff --git a/NEWS b/NEWS
index d057c06..495bde0 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,11 @@ Version 2.25
   TR.  Note that not all functions from that TR are supported by the GNU C
   Library.
 
+* The feature test macro __STDC_WANT_IEC_60559_BFP_EXT__, from ISO/IEC TS
+  18661-1:2014, is supported to enable declarations of functions and macros
+  from that TS.  Note that most features from that TS are not supported by
+  the GNU C Library.
+
 Security related changes:
 
   [Add security related changes here]
diff --git a/bits/libc-header-start.h b/bits/libc-header-start.h
index c666307..6a58505 100644
--- a/bits/libc-header-start.h
+++ b/bits/libc-header-start.h
@@ -41,3 +41,12 @@
 #else
 # define __GLIBC_USE_LIB_EXT2 0
 #endif
+
+/* ISO/IEC TS 18661-1:2014 defines the __STDC_WANT_IEC_60559_BFP_EXT__
+   macro.  */
+#undef __GLIBC_USE_IEC_60559_BFP_EXT
+#if defined __USE_GNU || defined __STDC_WANT_IEC_60559_BFP_EXT__
+# define __GLIBC_USE_IEC_60559_BFP_EXT 1
+#else
+# define __GLIBC_USE_IEC_60559_BFP_EXT 0
+#endif
diff --git a/include/features.h b/include/features.h
index 4040141..f2cd148 100644
--- a/include/features.h
+++ b/include/features.h
@@ -25,6 +25,7 @@
    _ISOC99_SOURCE	Extensions to ISO C89 from ISO C99.
    _ISOC11_SOURCE	Extensions to ISO C99 from ISO C11.
    __STDC_WANT_LIB_EXT2__ Extensions to ISO C99 from TR 27431-2:2010.
+   __STDC_WANT_IEC_60559_BFP_EXT__ Extensions to ISO C11 from TS 18661-1:2014.
    _POSIX_SOURCE	IEEE Std 1003.1.
    _POSIX_C_SOURCE	If ==1, like _POSIX_SOURCE; if >=2 add IEEE Std 1003.2;
 			if >=199309L, add IEEE Std 1003.1b-1993;
diff --git a/manual/arith.texi b/manual/arith.texi
index f54b1ec..3d8bdd8 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -397,12 +397,11 @@ to
 @end deftypefn
 
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefn {Macro} int issignaling (@emph{float-type} @var{x})
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 This macro returns a nonzero value if @var{x} is a signaling NaN
-(sNaN).  It is based on draft TS 18661 and currently enabled as a GNU
-extension.
+(sNaN).  It is from TS 18661-1:2014.
 @end deftypefn
 
 Another set of floating-point classification functions was provided by
@@ -1703,13 +1702,13 @@ double}.
 @end deftypefun
 
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefun double nextup (double @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx float nextupf (float @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx {long double} nextupl (long double @var{x})
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 The @code{nextup} function returns the next representable neighbor of @var{x}
@@ -1718,18 +1717,18 @@ subnormal number in the type of @var{x} the function returns @code{-0}.  If
 @math{@var{x} = @code{0}} the function returns the smallest positive subnormal
 number in the type of @var{x}.  If @var{x} is NaN, NaN is returned.
 If @var{x} is @math{+@infinity{}}, @math{+@infinity{}} is returned.
-@code{nextup} is based on TS 18661 and currently enabled as a GNU extension.
+@code{nextup} from TS 18661-1:2014.
 @code{nextup} never raises an exception except for signaling NaNs.
 @end deftypefun
 
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefun double nextdown (double @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx float nextdownf (float @var{x})
 @comment math.h
-@comment GNU
+@comment ISO
 @deftypefunx {long double} nextdownl (long double @var{x})
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
 The @code{nextdown} function returns the next representable neighbor of @var{x}
@@ -1738,7 +1737,7 @@ subnormal number in the type of @var{x} the function returns @code{+0}.  If
 @math{@var{x} = @code{0}} the function returns the smallest negative subnormal
 number in the type of @var{x}.  If @var{x} is NaN, NaN is returned.
 If @var{x} is @math{-@infinity{}}, @math{-@infinity{}} is returned.
-@code{nextdown} is based on TS 18661 and currently enabled as a GNU extension.
+@code{nextdown} is from TS 18661-1:2014.
 @code{nextdown} never raises an exception except for signaling NaNs.
 @end deftypefun
 
diff --git a/manual/creature.texi b/manual/creature.texi
index 65c5928..61b17ce 100644
--- a/manual/creature.texi
+++ b/manual/creature.texi
@@ -174,6 +174,15 @@ of the features from this TR are supported by @theglibc{}.
 @end defvr
 
 @comment (none)
+@comment ISO
+@defvr Macro __STDC_WANT_IEC_60559_BFP_EXT__
+If you define this macro, features from ISO/IEC TS 18661-1:2014
+(Floating-point extensions for C: Binary floating-point arithmetic)
+are enabled.  Only some of the features from this TS are supported by
+@theglibc{}.
+@end defvr
+
+@comment (none)
 @comment GNU
 @defvr Macro _GNU_SOURCE
 If you define this macro, everything is included: @w{ISO C89}, @w{ISO
diff --git a/math/bits/mathcalls.h b/math/bits/mathcalls.h
index e2cf49f..e1c0521 100644
--- a/math/bits/mathcalls.h
+++ b/math/bits/mathcalls.h
@@ -294,7 +294,7 @@ __MATHCALLX (nextafter,, (_Mdouble_ __x, _Mdouble_ __y), (__const__));
 __MATHCALLX (nexttoward,, (_Mdouble_ __x, long double __y), (__const__));
 # endif
 
-#ifdef __USE_GNU
+#if __GLIBC_USE (IEC_60559_BFP_EXT)
 /* Return X - epsilon.  */
 __MATHCALL (nextdown,, (_Mdouble_ __x));
 /* Return X + epsilon.  */
@@ -377,7 +377,7 @@ __MATHCALL (fma,, (_Mdouble_ __x, _Mdouble_ __y, _Mdouble_ __z));
 __END_NAMESPACE_C99
 #endif
 
-#ifdef __USE_GNU
+#if __GLIBC_USE (IEC_60559_BFP_EXT)
 /* Test for signaling NaN.  */
 __MATHDECL_1 (int, __issignaling,, (_Mdouble_ __value))
      __attribute__ ((__const__));
diff --git a/math/math.h b/math/math.h
index 4724b10..ff9d70a 100644
--- a/math/math.h
+++ b/math/math.h
@@ -23,7 +23,8 @@
 #ifndef	_MATH_H
 #define	_MATH_H	1
 
-#include <features.h>
+#define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
+#include <bits/libc-header-start.h>
 
 __BEGIN_DECLS
 
@@ -328,7 +329,7 @@ enum
 
 #endif /* Use ISO C99.  */
 
-#ifdef __USE_GNU
+#if __GLIBC_USE (IEC_60559_BFP_EXT)
 /* Return nonzero value if X is a signaling NaN.  */
 # ifdef __NO_LONG_DOUBLE_MATH
 #  define issignaling(x) \
@@ -340,7 +341,7 @@ enum
       : sizeof (x) == sizeof (double)					      \
       ? __issignaling (x) : __issignalingl (x))
 # endif
-#endif /* Use GNU.  */
+#endif /* Use IEC_60559_BFP_EXT.  */
 
 #ifdef	__USE_MISC
 /* Support for various different standard error handling behaviors.  */
