diff --git a/ChangeLog b/ChangeLog
index da396fff20..32bbcf2e34 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2017-09-22  Jonathan Wakely  <jwakely@redhat.com>
+
+	[BZ #21326]
+	* include/features.h [__cplusplus >= 201703] (__USE_ISOC11): Define.
+	[__cplusplus >= 201103] (__USE_ISOC99): Define.
+	* math/Makefile (test-math-cxx11): New test.
+	* math/test-math-cxx11.cc: New file.
+
 2017-10-08  Christian Brauner  <christian.brauner@ubuntu.com>
 
 	* login/openpty.c (openpty): Close slave pty file descriptor on error.
diff --git a/include/features.h b/include/features.h
index c063b33b49..22735ec117 100644
--- a/include/features.h
+++ b/include/features.h
@@ -76,6 +76,7 @@
    __USE_ISOC11		Define ISO C11 things.
    __USE_ISOC99		Define ISO C99 things.
    __USE_ISOC95		Define ISO C90 AMD1 (C95) things.
+   __USE_ISOCXX11	Define ISO C++11 things.
    __USE_POSIX		Define IEEE Std 1003.1 things.
    __USE_POSIX2		Define IEEE Std 1003.2 things.
    __USE_POSIX199309	Define IEEE Std 1003.1, and .1b things.
@@ -238,13 +239,17 @@
 # define __USE_ISOC95	1
 #endif
 
+#ifdef __cplusplus
+/* This is to enable compatibility for ISO C++17.  */
+# if __cplusplus >= 201703L
+#  define __USE_ISOC11	1
+# endif
 /* This is to enable compatibility for ISO C++11.
-
-   So far g++ does not provide a macro.  Check the temporary macro for
-   now, too.  */
-#if ((defined __cplusplus && __cplusplus >= 201103L)			      \
-     || defined __GXX_EXPERIMENTAL_CXX0X__)
-# define __USE_ISOCXX11	1
+   Check the temporary macro for now, too.  */
+# if __cplusplus >= 201103L || defined __GXX_EXPERIMENTAL_CXX0X__
+#  define __USE_ISOCXX11	1
+#  define __USE_ISOC99	1
+# endif
 #endif
 
 /* If none of the ANSI/POSIX macros are defined, or if _DEFAULT_SOURCE
diff --git a/math/Makefile b/math/Makefile
index 008eeb2d18..d4f9e6b6e9 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -209,7 +209,7 @@ tests-static += atest-exp atest-sincos atest-exp2
 
 ifneq (,$(CXX))
 tests += test-math-isinff test-math-iszero test-math-issignaling \
-	 test-math-iscanonical
+	 test-math-iscanonical test-math-cxx11
 endif
 
 ifneq (no,$(PERL))
@@ -354,6 +354,8 @@ CFLAGS-test-signgam-ullong-init.c = -std=c99
 CFLAGS-test-signgam-ullong-static.c = -std=c99
 CFLAGS-test-signgam-ullong-init-static.c = -std=c99
 
+CFLAGS-test-math-cxx11.cc = -std=c++11
+
 CFLAGS-test-math-isinff.cc = -std=gnu++11
 CFLAGS-test-math-iszero.cc = -std=gnu++11
 CFLAGS-test-math-issignaling.cc = -std=gnu++11
diff --git a/math/test-math-cxx11.cc b/math/test-math-cxx11.cc
new file mode 100644
index 0000000000..5d93e668e6
--- /dev/null
+++ b/math/test-math-cxx11.cc
@@ -0,0 +1,161 @@
+/* Test C99 math functions are available in C++11 without _GNU_SOURCE.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Jonathan Wakely <jwakely@redhat.com>, 2017.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#undef _GNU_SOURCE
+#undef _DEFAULT_SOURCE
+#undef _XOPEN_SOURCE
+#undef _POSIX_SOURCE
+#undef _POSIX_C_SOURCE
+// __STRICT_ANSI__ gets defined by -std=c++11 in CFLAGS
+#include <math.h>
+#include <stdio.h>
+
+static int
+do_test (void)
+{
+#ifdef _GNU_SOURCE
+  printf ("FAIL: _GNU_SOURCE is defined.\n");
+  return 1;
+#endif
+
+#if __cplusplus >= 201103L
+  /* Verify that C11 math functions and types are defined for C++11,
+     without _GNU_SOURCE being defined. [BZ #21326] */
+  (void) FP_INFINITE;
+  (void) FP_NAN;
+  (void) FP_NORMAL;
+  (void) FP_SUBNORMAL;
+  (void) FP_ZERO;
+  double_t d = 1.0;
+  (void) d;
+  float_t f = 1.0f;
+  (void) f;
+  (void) acosh;
+  (void) acoshf;
+  (void) acoshl;
+  (void) asinh;
+  (void) asinhf;
+  (void) asinhl;
+  (void) atanh;
+  (void) atanhf;
+  (void) atanhl;
+  (void) cbrt;
+  (void) cbrtf;
+  (void) cbrtl;
+  (void) copysign;
+  (void) copysignf;
+  (void) copysignl;
+  (void) erf;
+  (void) erff;
+  (void) erfl;
+  (void) erfc;
+  (void) erfcf;
+  (void) erfcl;
+  (void) exp2;
+  (void) exp2f;
+  (void) exp2l;
+  (void) expm1;
+  (void) expm1f;
+  (void) expm1l;
+  (void) fdim;
+  (void) fdimf;
+  (void) fdiml;
+  (void) fma;
+  (void) fmaf;
+  (void) fmal;
+  (void) fmax;
+  (void) fmaxf;
+  (void) fmaxl;
+  (void) fmin;
+  (void) fminf;
+  (void) fminl;
+  (void) hypot;
+  (void) hypotf;
+  (void) hypotl;
+  (void) ilogb;
+  (void) ilogbf;
+  (void) ilogbl;
+  (void) lgamma;
+  (void) lgammaf;
+  (void) lgammal;
+  (void) llrint;
+  (void) llrintf;
+  (void) llrintl;
+  (void) llround;
+  (void) llroundf;
+  (void) llroundl;
+  (void) log1p;
+  (void) log1pf;
+  (void) log1pl;
+  (void) log2;
+  (void) log2f;
+  (void) log2l;
+  (void) logb;
+  (void) logbf;
+  (void) logbl;
+  (void) lrint;
+  (void) lrintf;
+  (void) lrintl;
+  (void) lround;
+  (void) lroundf;
+  (void) lroundl;
+  (void) nan;
+  (void) nanf;
+  (void) nanl;
+  (void) nearbyint;
+  (void) nearbyintf;
+  (void) nearbyintl;
+  (void) nextafter;
+  (void) nextafterf;
+  (void) nextafterl;
+  (void) nexttoward;
+  (void) nexttowardf;
+  (void) nexttowardl;
+  (void) remainder;
+  (void) remainderf;
+  (void) remainderl;
+  (void) remquo;
+  (void) remquof;
+  (void) remquol;
+  (void) rint;
+  (void) rintf;
+  (void) rintl;
+  (void) round;
+  (void) roundf;
+  (void) roundl;
+  (void) scalbln;
+  (void) scalblnf;
+  (void) scalblnl;
+  (void) scalbn;
+  (void) scalbnf;
+  (void) scalbnl;
+  (void) tgamma;
+  (void) tgammaf;
+  (void) tgammal;
+  (void) trunc;
+  (void) truncf;
+  (void) truncl;
+  printf ("PASS: C11 math functions present in C++11 without _GNU_SOURCE.\n");
+#else
+  printf ("UNSUPPORTED: C++11 not enabled.\n");
+#endif
+  return 0;
+}
+
+#include <support/test-driver.c>
