diff --git a/NEWS b/NEWS
index f59a27d..23ca5ab 100644
--- a/NEWS
+++ b/NEWS
@@ -49,6 +49,10 @@ Version 2.25
   UINTMAX_WIDTH, PTRDIFF_WIDTH, SIG_ATOMIC_WIDTH, SIZE_WIDTH, WCHAR_WIDTH,
   WINT_WIDTH.
 
+* New <math.h> features are added from TS 18661-1:2014:
+
+  - Classification macros: issubnormal.
+
 * The <sys/quota.h> header now includes the <linux/quota.h> header.  Support
   for the Linux quota interface which predates kernel version 2.4.22 has
   been removed.
diff --git a/manual/arith.texi b/manual/arith.texi
index dc3c367..bfa236a 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -406,6 +406,14 @@ This macro returns a nonzero value if @var{x} is a signaling NaN
 (sNaN).  It is from TS 18661-1:2014.
 @end deftypefn
 
+@comment math.h
+@comment ISO
+@deftypefn {Macro} int issubnormal (@emph{float-type} @var{x})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This macro returns a nonzero value if @var{x} is subnormal.  It is
+from TS 18661-1:2014.
+@end deftypefn
+
 Another set of floating-point classification functions was provided by
 BSD.  @Theglibc{} also supports these functions; however, we
 recommend that you use the ISO C99 macros in new code.  Those are standard
diff --git a/manual/libm-err-tab.pl b/manual/libm-err-tab.pl
index c2792c5..adeadb8 100755
--- a/manual/libm-err-tab.pl
+++ b/manual/libm-err-tab.pl
@@ -77,9 +77,9 @@ use vars qw (%results @all_floats %suffices @all_functions);
     "nextup", "pow", "remainder", "remquo", "rint", "round", "scalb",
     "scalbn", "sin", "sincos", "sinh", "sqrt", "tan", "tanh", "tgamma",
     "trunc", "y0", "y1", "yn" );
-# fpclassify, isnormal, isfinite, isinf, isnan, issignaling, signbit,
-# isgreater, isgreaterequal, isless, islessequal, islessgreater, isunordered
-# are not tabulated.
+# fpclassify, isnormal, isfinite, isinf, isnan, issignaling,
+# issubnormal, signbit, isgreater, isgreaterequal, isless,
+# islessequal, islessgreater, isunordered are not tabulated.
 
 if ($#ARGV == 0) {
   $sources = $ARGV[0];
diff --git a/math/libm-test.inc b/math/libm-test.inc
index e4fcb5a..385ec5c 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -46,7 +46,7 @@
    cbrt, ceil, copysign, cos, cosh, drem, erf, erfc, exp, exp10, exp2, expm1,
    fabs, fdim, finite, floor, fma, fmax, fmin, fmod, fpclassify,
    frexp, gamma, hypot,
-   ilogb, isfinite, isinf, isnan, isnormal, issignaling,
+   ilogb, isfinite, isinf, isnan, isnormal, issignaling, issubnormal,
    isless, islessequal, isgreater, isgreaterequal, islessgreater, isunordered,
    j0, j1, jn,
    ldexp, lgamma, log, log10, log1p, log2, logb,
@@ -8587,6 +8587,31 @@ issignaling_test (void)
   ALL_RM_TEST (issignaling, 1, issignaling_test_data, RUN_TEST_LOOP_f_b_tg, END);
 }
 
+static const struct test_f_i_data issubnormal_test_data[] =
+  {
+    TEST_f_b (issubnormal, 0, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, minus_zero, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, 10, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, min_subnorm_value, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -min_subnorm_value, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, min_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -min_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, max_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -max_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, plus_infty, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, minus_infty, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, qnan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -qnan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, snan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_f_b (issubnormal, -snan_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+  };
+
+static void
+issubnormal_test (void)
+{
+  ALL_RM_TEST (issubnormal, 1, issubnormal_test_data, RUN_TEST_LOOP_f_b_tg, END);
+}
+
 static const struct test_ff_i_data isunordered_test_data[] =
   {
     TEST_ff_i (isunordered, minus_zero, minus_zero, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
@@ -12668,6 +12693,7 @@ main (int argc, char **argv)
   isnan_test ();
   isnormal_test ();
   issignaling_test ();
+  issubnormal_test ();
   signbit_test ();
 
   /* Trigonometric functions:  */
diff --git a/math/math.h b/math/math.h
index 2f77dee..064cc56 100644
--- a/math/math.h
+++ b/math/math.h
@@ -328,6 +328,9 @@ enum
       : sizeof (x) == sizeof (double)					      \
       ? __issignaling (x) : __issignalingl (x))
 # endif
+
+/* Return nonzero value if X is subnormal.  */
+# define issubnormal(x) (fpclassify (x) == FP_SUBNORMAL)
 #endif /* Use IEC_60559_BFP_EXT.  */
 
 #ifdef	__USE_MISC
