diff --git a/Makefile b/Makefile
index 4478c97..e26774d 100644
--- a/Makefile
+++ b/Makefile
@@ -318,6 +318,29 @@ $(objpfx)begin-end-check.out:
scripts/begin-end-check.pl
 	$(evaluate-test)
 endif

+ifneq "$(headers)" ""
+# Special test of all the installed headers in this directory.
+tests-special += $(objpfx)check-installed-headers-c.out
+libof-check-installed-headers-c := nonlib
+$(objpfx)check-installed-headers-c.out: \
+    scripts/check-installed-headers.sh $(headers)
+	$(SHELL) $(..)scripts/check-installed-headers.sh c \
+	  "$(CC) $(filter-out -std=%,$(CFLAGS)) -D_ISOMAC $(+includes)" \
+	  $(headers) > $@; \
+	$(evaluate-test)
+
+ifneq "$(CXX)" ""
+tests-special += $(objpfx)check-installed-headers-cxx.out
+libof-check-installed-headers-cxx := nonlib
+$(objpfx)check-installed-headers-cxx.out: \
+    scripts/check-installed-headers.sh $(headers)
+	$(SHELL) $(..)scripts/check-installed-headers.sh c++ \
+	  "$(CXX) $(filter-out -std=%,$(CXXFLAGS)) -D_ISOMAC $(+includes)" \
+	  $(headers) > $@; \
+	$(evaluate-test)
+endif
+endif
+
 define summarize-tests
 @egrep -v '^(PASS|XFAIL):' $(objpfx)$1 || true
 @echo "Summary of test results$2:"
diff --git a/Rules b/Rules
index 8306d36..342d659 100644
--- a/Rules
+++ b/Rules
@@ -80,6 +80,29 @@ $(common-objpfx)dummy.c:
 	(echo 'extern void __dummy__ (void);'; \
 	 echo 'void __dummy__ (void) { }') > $@
 common-generated += dummy.o dummy.c
+
+ifneq "$(headers)" ""
+# Special test of all the installed headers in this directory.
+tests-special += $(objpfx)check-installed-headers-c.out
+libof-check-installed-headers-c := nonlib
+$(objpfx)check-installed-headers-c.out: \
+    $(..)scripts/check-installed-headers.sh $(headers)
+	$(SHELL) $(..)scripts/check-installed-headers.sh c \
+	  "$(CC) $(filter-out -std=%,$(CFLAGS)) -D_ISOMAC $(+includes)" \
+	  $(headers) > $@; \
+	$(evaluate-test)
+
+ifneq "$(CXX)" ""
+tests-special += $(objpfx)check-installed-headers-cxx.out
+libof-check-installed-headers-cxx := nonlib
+$(objpfx)check-installed-headers-cxx.out: \
+    $(..)scripts/check-installed-headers.sh $(headers)
+	$(SHELL) $(..)scripts/check-installed-headers.sh c++ \
+	  "$(CXX) $(filter-out -std=%,$(CXXFLAGS)) -D_ISOMAC $(+includes)" \
+	  $(headers) > $@; \
+	$(evaluate-test)
+endif
+endif
 
 # This makes all the auxiliary and test programs.

diff --git a/include/aliases.h b/include/aliases.h
index f7cfafc..ece69eb 100644
--- a/include/aliases.h
+++ b/include/aliases.h
@@ -1,6 +1,8 @@
 #ifndef _ALIASES_H
 #include <inet/aliases.h>

+# ifndef _ISOMAC
+
 extern int __getaliasent_r (struct aliasent *__restrict __result_buf,
 			    char *__restrict __buffer, size_t __buflen,
 			    struct aliasent **__restrict __result)
@@ -34,4 +36,5 @@ DECLARE_NSS_PROTOTYPES (nis)
 DECLARE_NSS_PROTOTYPES (nisplus)
 #undef DECLARE_NSS_PROTOTYPES

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/alloca.h b/include/alloca.h
index 0150025..fd90664 100644
--- a/include/alloca.h
+++ b/include/alloca.h
@@ -1,6 +1,9 @@
 #ifndef _ALLOCA_H

 #include <stdlib/alloca.h>
+
+# ifndef _ISOMAC
+
 #include <stackinfo.h>

 #undef	__alloca
@@ -73,4 +76,5 @@ libc_hidden_proto (__libc_alloca_cutoff)
      extend_alloca (buf, len, s__); })
 #endif

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/argz.h b/include/argz.h
index 4eab0b6..0388c23 100644
--- a/include/argz.h
+++ b/include/argz.h
@@ -2,8 +2,11 @@

 #include <string/argz.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (argz_delete)
 libc_hidden_proto (__argz_count)
 libc_hidden_proto (__argz_stringify)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/arpa/nameser.h b/include/arpa/nameser.h
index ce6f023..cd7ab6e 100644
--- a/include/arpa/nameser.h
+++ b/include/arpa/nameser.h
@@ -2,6 +2,8 @@

 #include <resolv/arpa/nameser.h>

+# ifndef _ISOMAC
+
 /* If the machine allows unaligned access we can do better than using
    the NS_GET16, NS_GET32, NS_PUT16, and NS_PUT32 macros from the
    installed header.  */
@@ -74,4 +76,5 @@ libresolv_hidden_proto (ns_samename)
 libresolv_hidden_proto (ns_makecanon)
 libresolv_hidden_proto (ns_format_ttl)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/arpa/nameser_compat.h b/include/arpa/nameser_compat.h
index 2e735ed..6928000 100644
--- a/include/arpa/nameser_compat.h
+++ b/include/arpa/nameser_compat.h
@@ -1,8 +1,11 @@
 #ifndef _ARPA_NAMESER_COMPAT_
 #include <resolv/arpa/nameser_compat.h>

+# ifndef _ISOMAC
+
 /* Picksome unused number to represent lookups of IPv4 and IPv6 (i.e.,
    T_A and T_AAAA).  */
 #define T_UNSPEC 62321

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/elf.h b/include/elf.h
index 60658c6..f06a33f 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -1,5 +1,8 @@
 #ifndef _ELF_H
-# include <elf/elf.h>
+#include <elf/elf.h>
+
+# ifndef _ISOMAC
+
 /* Some information which is not meant for the public and therefore not
    in <elf.h>.  */
 # include <dl-dtprocnum.h>
@@ -9,4 +12,6 @@
 # define DT_1_SUPPORTED_MASK \
    (DF_1_NOW | DF_1_NODELETE | DF_1_INITFIRST | DF_1_NOOPEN \
     | DF_1_ORIGIN | DF_1_NODEFLIB)
-#endif
+
+# endif /* !_ISOMAC */
+#endif /* elf.h */
diff --git a/include/envz.h b/include/envz.h
index 8cfd9b5..633fcc6 100644
--- a/include/envz.h
+++ b/include/envz.h
@@ -2,7 +2,10 @@

 #include <string/envz.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (envz_entry)
 libc_hidden_proto (envz_remove)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/err.h b/include/err.h
index 737dfc1..3828559 100644
--- a/include/err.h
+++ b/include/err.h
@@ -1,8 +1,14 @@
+#ifndef _ERR_H
 #include <misc/err.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (warn)
 libc_hidden_proto (warnx)
 libc_hidden_proto (vwarn)
 libc_hidden_proto (vwarnx)
 libc_hidden_proto (verr)
 libc_hidden_proto (verrx)
+
+# endif /* !_ISOMAC */
+#endif /* err.h */
diff --git a/include/execinfo.h b/include/execinfo.h
index c929821..0b132b0 100644
--- a/include/execinfo.h
+++ b/include/execinfo.h
@@ -1,6 +1,8 @@
 #ifndef _EXECINFO_H
 #include <debug/execinfo.h>

+# ifndef _ISOMAC
+
 extern int __backtrace (void **__array, int __size);
 libc_hidden_proto (__backtrace)

@@ -10,4 +12,5 @@ extern void __backtrace_symbols_fd (void *const
*__array, int __size,
 				    int __fd);
 libc_hidden_proto (__backtrace_symbols_fd)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/fpu_control.h b/include/fpu_control.h
index d0b5e9c..4498a83 100644
--- a/include/fpu_control.h
+++ b/include/fpu_control.h
@@ -1,4 +1,10 @@
+#ifndef _FPU_CONTROL_H
 #include_next <fpu_control.h>

+# ifndef _ISOMAC
+
 /* Called at startup.  It can be used to manipulate fpu control
register.  */
 extern void __setfpucw (fpu_control_t);
+
+# endif /* !_ISOMAC */
+#endif /* fpu_control.h */
diff --git a/include/getopt.h b/include/getopt.h
index 6f2693d..c094972 100644
--- a/include/getopt.h
+++ b/include/getopt.h
@@ -3,11 +3,10 @@
 #include <features.h>		/* Get __GNU_LIBRARY__ defined now.  */
 #include <posix/getopt.h>

-# ifdef _GETOPT_H
+# if defined _GETOPT_H && !defined _ISOMAC

 /* Now define the internal interfaces.  */
 extern void __getopt_clean_environment (char **__env);

-# endif
-
+# endif /* _GETOPT_H && !_ISOMAC */
 #endif
diff --git a/include/gshadow.h b/include/gshadow.h
index 8a981f6..532801a 100644
--- a/include/gshadow.h
+++ b/include/gshadow.h
@@ -1,6 +1,8 @@
 #ifndef _GSHADOW_H
 #include <gshadow/gshadow.h>

+# ifndef _ISOMAC
+
 extern int __fgetsgent_r (FILE *stream, struct sgrp *resbuf, char *buffer,
 			  size_t buflen, struct sgrp **result);
 extern int __sgetsgent_r (const char *string, struct sgrp *resbuf,
@@ -12,4 +14,5 @@ extern int _nss_files_parse_sgent (char *line, struct
sgrp *result,
                                    size_t datalen, int *errnop);
 libc_hidden_proto (_nss_files_parse_sgent)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/ifaddrs.h b/include/ifaddrs.h
index 2787f21..54f4b7a 100644
--- a/include/ifaddrs.h
+++ b/include/ifaddrs.h
@@ -1,5 +1,8 @@
 #ifndef _IFADDRS_H
 #include <inet/ifaddrs.h>
+
+# ifndef _ISOMAC
+
 #include <stdbool.h>
 #include <stdint.h>

@@ -30,4 +33,5 @@ extern void __check_native (uint32_t a1_index, int
*a1_native,
 extern uint32_t __bump_nl_timestamp (void) attribute_hidden;
 #endif

+# endif /* !_ISOMAC */
 #endif	/* ifaddrs.h */
diff --git a/include/libintl.h b/include/libintl.h
index 0551a04..9a11367 100644
--- a/include/libintl.h
+++ b/include/libintl.h
@@ -1,5 +1,8 @@
 #ifndef _LIBINTL_H
 #include <intl/libintl.h>
+
+# ifndef _ISOMAC
+
 #include <locale.h>

 /* Now define the internal interfaces.  */
@@ -46,4 +49,5 @@ libc_hidden_proto (_libc_intl_domainname)
 # define _(msgid) \
   __dcgettext (_libc_intl_domainname, msgid, LC_MESSAGES)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/link.h b/include/link.h
index 32a7392..0558442 100644
--- a/include/link.h
+++ b/include/link.h
@@ -24,12 +24,18 @@
 # error this should be impossible
 #endif

+# ifndef _ISOMAC
 /* Get most of the contents from the public header, but we define a
    different `struct link_map' type for private use.  The la_objopen
    prototype uses the type, so we have to declare it separately.  */
-#define link_map	link_map_public
-#define la_objopen	la_objopen_wrongproto
+#  define link_map	link_map_public
+#  define la_objopen	la_objopen_wrongproto
+# endif
+
 #include <elf/link.h>
+
+# ifndef _ISOMAC
+
 #undef	link_map
 #undef	la_objopen

@@ -341,4 +347,5 @@ extern int __dl_iterate_phdr (int (*callback)
(struct dl_phdr_info *info,
    `ELF64_R_TYPE'.  */
 #define ELFW(type)	_ElfW (ELF, __ELF_NATIVE_CLASS, type)

+# endif /* !_ISOMAC */
 #endif /* include/link.h */
diff --git a/include/malloc.h b/include/malloc.h
index 42fc8ed..70d32c7 100644
--- a/include/malloc.h
+++ b/include/malloc.h
@@ -1,6 +1,7 @@
 #ifndef _MALLOC_H
 #include <malloc/malloc.h>

+# ifndef _ISOMAC

 /* In the GNU libc we rename the global variable
    `__malloc_initialized' to `__libc_malloc_initialized'.  */
@@ -11,4 +12,5 @@ extern int __malloc_initialized attribute_hidden;
 struct malloc_state;
 typedef struct malloc_state *mstate;

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/mcheck.h b/include/mcheck.h
index b0037a7..8883c3d 100644
--- a/include/mcheck.h
+++ b/include/mcheck.h
@@ -2,7 +2,10 @@

 #include <malloc/mcheck.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (mcheck)
 libc_hidden_proto (mcheck_check_all)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/mntent.h b/include/mntent.h
index b34674a..169210f 100644
--- a/include/mntent.h
+++ b/include/mntent.h
@@ -1,6 +1,8 @@
 #ifndef _MNTENT_H
 #include <misc/mntent.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern FILE *__setmntent (const char *__file, const char *__mode);
 extern struct mntent *__getmntent_r (FILE *__stream,
@@ -14,4 +16,5 @@ libc_hidden_proto (__setmntent)
 libc_hidden_proto (__getmntent_r)
 libc_hidden_proto (__endmntent)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/netinet/ether.h b/include/netinet/ether.h
index 2efe4c0..8bfe7e0 100644
--- a/include/netinet/ether.h
+++ b/include/netinet/ether.h
@@ -1,6 +1,8 @@
 #ifndef _NETINET_ETHER_H
 #include <inet/netinet/ether.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (ether_aton_r)
 libc_hidden_proto (ether_ntoa_r)

@@ -39,4 +41,5 @@ DECLARE_NSS_PROTOTYPES (nisplus)

 #undef DECLARE_NSS_PROTOTYPES

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/nss.h b/include/nss.h
index 1e8cc39..6358a10 100644
--- a/include/nss.h
+++ b/include/nss.h
@@ -1,6 +1,8 @@
 #ifndef _NSS_H
 #include <nss/nss.h>

+# ifndef _ISOMAC
+
 #define NSS_INVALID_FIELD_CHARACTERS ":\n"
 extern const char __nss_invalid_field_characters[] attribute_hidden;

@@ -11,4 +13,5 @@ _Bool __nss_valid_list_field (char **list)
 const char *__nss_rewrite_field (const char *value, char **to_be_freed)
   attribute_hidden internal_function;

+# endif /* !_ISOMAC */
 #endif /* _NSS_H */
diff --git a/include/obstack.h b/include/obstack.h
index 349d59b..fe2e595 100644
--- a/include/obstack.h
+++ b/include/obstack.h
@@ -1,3 +1,9 @@
+#ifndef _OBSTACK_H
 #include <malloc/obstack.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (_obstack_newchunk)
+
+# endif /* !_ISOMAC */
+#endif /* obstack.h */
diff --git a/include/printf.h b/include/printf.h
index b12b5dc..984f263 100644
--- a/include/printf.h
+++ b/include/printf.h
@@ -1,6 +1,9 @@
 #ifndef	_PRINTF_H

 #include <stdio-common/printf.h>
+
+# ifndef _ISOMAC
+
 #include <xlocale.h>

 /* Now define the internal interfaces.  */
@@ -13,4 +16,5 @@ extern int __printf_fp_l (FILE *, locale_t, const
struct printf_info *,
 			  const void *const *);
 libc_hidden_proto (__printf_fp_l)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/pty.h b/include/pty.h
index a91be80..4979bb7 100644
--- a/include/pty.h
+++ b/include/pty.h
@@ -1,6 +1,9 @@
 #ifndef _PTY_H
 #include <login/pty.h>

+# ifndef _ISOMAC
+
 libutil_hidden_proto (openpty)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/resolv.h b/include/resolv.h
index 52ac218..699cc81 100644
--- a/include/resolv.h
+++ b/include/resolv.h
@@ -1,17 +1,19 @@
 #ifndef _RESOLV_H_

-#define RES_SET_H_ERRNO(r,x)			\
+# ifndef _ISOMAC
+#  include <stdbool.h>
+#  define RES_SET_H_ERRNO(r,x)			\
   do						\
     {						\
       (r)->res_h_errno = x;			\
       __set_h_errno(x);				\
     }						\
   while (0)
+# endif

-#include <stdbool.h>
 #include <resolv/resolv.h>

-#ifdef _RESOLV_H_
+# if defined _RESOLV_H_ && !defined _ISOMAC

 # if IS_IN (libc)
 #  define __resp __libc_resp
@@ -97,6 +99,5 @@ libresolv_hidden_proto (__p_secstodate)
 extern const char *_res_opcodes[];
 libresolv_hidden_proto (_res_opcodes)

-#endif
-
+# endif /* _RESOLV_H_ && !_ISOMAC */
 #endif
diff --git a/include/rpc/auth.h b/include/rpc/auth.h
index 0219fd9..2e55cce 100644
--- a/include/rpc/auth.h
+++ b/include/rpc/auth.h
@@ -1,6 +1,8 @@
 #ifndef _RPC_AUTH_H
 #include <sunrpc/rpc/auth.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (getnetname)
 libc_hidden_proto (netname2user)
 libc_hidden_proto (host2netname)
@@ -41,4 +43,5 @@ libc_hidden_proto (key_setnet)
 libc_hidden_proto (key_setsecret)
 libc_hidden_proto (netname2host)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/auth_des.h b/include/rpc/auth_des.h
index 0e9db1a..6afed56 100644
--- a/include/rpc/auth_des.h
+++ b/include/rpc/auth_des.h
@@ -2,6 +2,8 @@

 #include <sunrpc/rpc/auth_des.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (getpublickey)
 libc_hidden_proto (getsecretkey)
 libc_hidden_proto (rtime)
@@ -32,4 +34,5 @@ libc_hidden_proto (authdes_getucred)
 libc_hidden_proto (xdr_authdes_cred)
 libc_hidden_proto (xdr_authdes_verf)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/auth_unix.h b/include/rpc/auth_unix.h
index 07031c9..019efa2 100644
--- a/include/rpc/auth_unix.h
+++ b/include/rpc/auth_unix.h
@@ -1,3 +1,9 @@
+#ifndef _RPC_AUTH_UNIX_H
 #include <sunrpc/rpc/auth_unix.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (xdr_authunix_parms)
+
+# endif /* !_ISOMAC */
+#endif /* rpc/auth_unix.h */
diff --git a/include/rpc/clnt.h b/include/rpc/clnt.h
index d79a6a7..a397023 100644
--- a/include/rpc/clnt.h
+++ b/include/rpc/clnt.h
@@ -1,6 +1,8 @@
 #ifndef _RPC_CLNT_H
 #include <sunrpc/rpc/clnt.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern int _openchild (const char *command, FILE **fto, FILE **ffrom);

@@ -27,4 +29,5 @@ libc_hidden_proto (get_myaddress)
 libc_hidden_proto (clntunix_create)
 libc_hidden_proto (__libc_clntudp_bufcreate)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/des_crypt.h b/include/rpc/des_crypt.h
index 44f7e66..7a34957 100644
--- a/include/rpc/des_crypt.h
+++ b/include/rpc/des_crypt.h
@@ -1,6 +1,8 @@
 #ifndef __DES_CRYPT_H__
 #include <sunrpc/rpc/des_crypt.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */

 extern int xencrypt (char *secret, char *passwd);
@@ -12,4 +14,5 @@ libc_hidden_proto (cbc_crypt)
 libc_hidden_proto (xencrypt)
 libc_hidden_proto (xdecrypt)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/key_prot.h b/include/rpc/key_prot.h
index 29d14cc..4711a94 100644
--- a/include/rpc/key_prot.h
+++ b/include/rpc/key_prot.h
@@ -1,5 +1,8 @@
+#ifndef _KEY_PROT_H_RPCGEN
 #include <sunrpc/rpc/key_prot.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (xdr_cryptkeyarg)
 libc_hidden_proto (xdr_cryptkeyarg2)
 libc_hidden_proto (xdr_cryptkeyres)
@@ -10,3 +13,6 @@ libc_hidden_proto (xdr_keystatus)
 libc_hidden_proto (xdr_getcredres)
 libc_hidden_proto (xdr_netnamestr)
 libc_hidden_proto (xdr_unixcred)
+
+# endif /* !_ISOMAC */
+#endif /* rpc/key_prot.h */
diff --git a/include/rpc/netdb.h b/include/rpc/netdb.h
index 65af237..9b84668 100644
--- a/include/rpc/netdb.h
+++ b/include/rpc/netdb.h
@@ -1,6 +1,8 @@
 #ifndef _RPC_NETDB_H
 #include <sunrpc/rpc/netdb.h>

+# ifndef _ISOMAC
+
 extern int __getrpcbyname_r (const char *__name, struct rpcent
*__result_buf,
 			     char *__buffer, size_t __buflen,
 			     struct rpcent **__result);
@@ -48,4 +50,5 @@ DECLARE_NSS_PROTOTYPES (nisplus)

 #undef DECLARE_NSS_PROTOTYPES

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/pmap_clnt.h b/include/rpc/pmap_clnt.h
index 67628e0..ec907c2 100644
--- a/include/rpc/pmap_clnt.h
+++ b/include/rpc/pmap_clnt.h
@@ -1,5 +1,7 @@
 #ifndef _RPC_PMAP_CLNT_H
-# include <sunrpc/rpc/pmap_clnt.h>
+#include <sunrpc/rpc/pmap_clnt.h>
+
+# ifndef _ISOMAC

 libc_hidden_proto (pmap_getport)
 libc_hidden_proto (pmap_set)
@@ -18,4 +20,5 @@ libc_hidden_proto (clnt_broadcast)
 libc_hidden_proto (pmap_getmaps)
 libc_hidden_proto (pmap_rmtcall)

-#endif
+# endif /* !_ISOMAC */
+#endif /* rpc/pmap_clnt.h */
diff --git a/include/rpc/pmap_prot.h b/include/rpc/pmap_prot.h
index 2e9076e..a2573d1 100644
--- a/include/rpc/pmap_prot.h
+++ b/include/rpc/pmap_prot.h
@@ -1,4 +1,10 @@
+#ifndef _RPC_PMAP_PROT_H
 #include <sunrpc/rpc/pmap_prot.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (xdr_pmap)
 libc_hidden_proto (xdr_pmaplist)
+
+# endif /* !_ISOMAC */
+#endif /* rpc/pmap_prot.h */
diff --git a/include/rpc/pmap_rmt.h b/include/rpc/pmap_rmt.h
index e8822da..ae53a02 100644
--- a/include/rpc/pmap_rmt.h
+++ b/include/rpc/pmap_rmt.h
@@ -1,4 +1,10 @@
+#ifndef _RPC_PMAP_RMT_H
 #include <sunrpc/rpc/pmap_rmt.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (xdr_rmtcall_args)
 libc_hidden_proto (xdr_rmtcallres)
+
+# endif /* !_ISOMAC */
+#endif /* rpc/pmap_rmt.h */
diff --git a/include/rpc/rpc.h b/include/rpc/rpc.h
index 58bdef3..4c9ee82 100644
--- a/include/rpc/rpc.h
+++ b/include/rpc/rpc.h
@@ -1,5 +1,8 @@
 #ifndef _RPC_RPC_H
 #include <sunrpc/rpc/rpc.h>
+
+# ifndef _ISOMAC
+
 #include <libc-tsd.h>

 /* Now define the internal interfaces.  */
@@ -56,4 +59,5 @@ libc_hidden_proto (__rpc_thread_createerr)

 #endif /* _RPC_THREAD_SAFE_ */

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/rpc_msg.h b/include/rpc/rpc_msg.h
index be1f483..93c5ab8 100644
--- a/include/rpc/rpc_msg.h
+++ b/include/rpc/rpc_msg.h
@@ -1,6 +1,8 @@
 #ifndef _RPC_MSG_H
 #include <sunrpc/rpc/rpc_msg.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (_seterr_reply)

 /* Now define the internal interfaces.  */
@@ -14,4 +16,5 @@ libc_hidden_proto (xdr_callmsg)
 libc_hidden_proto (xdr_rejected_reply)
 libc_hidden_proto (xdr_replymsg)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/svc.h b/include/rpc/svc.h
index 61a8ab3..465bf44 100644
--- a/include/rpc/svc.h
+++ b/include/rpc/svc.h
@@ -1,6 +1,8 @@
 #ifndef _RPC_SVC_H
 #include <sunrpc/rpc/svc.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (xprt_register)
 libc_hidden_proto (xprt_unregister)
 libc_hidden_proto (svc_register)
@@ -37,4 +39,5 @@ libc_hidden_proto (svc_getreq_poll)

 extern void __svc_accept_failed (void) attribute_hidden;

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/svc_auth.h b/include/rpc/svc_auth.h
index 582bb31..2609d19 100644
--- a/include/rpc/svc_auth.h
+++ b/include/rpc/svc_auth.h
@@ -1,6 +1,8 @@
 #ifndef _RPC_SVC_AUTH_H
 #include <sunrpc/rpc/svc_auth.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern enum auth_stat _svcauth_unix (struct svc_req *rqst,
 				     struct rpc_msg *msg);
@@ -9,4 +11,5 @@ extern enum auth_stat _svcauth_short (struct svc_req *rqst,

 libc_hidden_proto (_authenticate)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpc/xdr.h b/include/rpc/xdr.h
index 57971d0..e1bff1c 100644
--- a/include/rpc/xdr.h
+++ b/include/rpc/xdr.h
@@ -1,5 +1,8 @@
+#ifndef _RPC_XDR_H
 #include <sunrpc/rpc/xdr.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (xdrstdio_create)
 libc_hidden_proto (xdr_array)
 libc_hidden_proto (xdr_bool)
@@ -45,3 +48,6 @@ libc_hidden_proto (xdr_int64_t)
 libc_hidden_proto (xdr_uint64_t)
 libc_hidden_proto (xdr_quad_t)
 libc_hidden_proto (xdr_u_quad_t)
+
+# endif /* !_ISOMAC */
+#endif /* rpc/xdr.h */
diff --git a/include/rpcsvc/nis_callback.h b/include/rpcsvc/nis_callback.h
index dfa9cd3..0515d07 100644
--- a/include/rpcsvc/nis_callback.h
+++ b/include/rpcsvc/nis_callback.h
@@ -1,7 +1,10 @@
 #ifndef _RPCSVC_NIS_CALLBACK_H
 #include <nis/rpcsvc/nis_callback.h>

+# ifndef _ISOMAC
+
 libnsl_hidden_proto (xdr_obj_p)
 libnsl_hidden_proto (xdr_cback_data)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpcsvc/nislib.h b/include/rpcsvc/nislib.h
index 635c513..05b1987 100644
--- a/include/rpcsvc/nislib.h
+++ b/include/rpcsvc/nislib.h
@@ -1,6 +1,8 @@
 #ifndef __RPCSVC_NISLIB_H__
 #include <nis/rpcsvc/nislib.h>

+# ifndef _ISOMAC
+
 libnsl_hidden_proto (nis_leaf_of_r)
 libnsl_hidden_proto (nis_name_of_r)
 libnsl_hidden_proto (nis_getnames)
@@ -44,4 +46,5 @@ libnsl_hidden_proto (nis_clone_object)

 extern const_nis_name __nis_domain_of (const_nis_name) __THROW;

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpcsvc/yp.h b/include/rpcsvc/yp.h
index 04a973e..b6d7c15 100644
--- a/include/rpcsvc/yp.h
+++ b/include/rpcsvc/yp.h
@@ -1,6 +1,8 @@
 #ifndef __RPCSVC_YP_H__
 #include <nis/rpcsvc/yp.h>

+# ifndef _ISOMAC
+
 libnsl_hidden_proto (xdr_ypstat)
 libnsl_hidden_proto (xdr_ypxfrstat)
 libnsl_hidden_proto (xdr_domainname)
@@ -23,4 +25,5 @@ libnsl_hidden_proto (xdr_ypresp_order)
 libnsl_hidden_proto (xdr_ypbind_resp)
 libnsl_hidden_proto (xdr_ypresp_master)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpcsvc/ypclnt.h b/include/rpcsvc/ypclnt.h
index b38dc6b..1b4e2f2 100644
--- a/include/rpcsvc/ypclnt.h
+++ b/include/rpcsvc/ypclnt.h
@@ -1,10 +1,13 @@
 #ifndef __RPCSVC_YPCLNT_H__
 #include <nis/rpcsvc/ypclnt.h>

+# ifndef _ISOMAC
+
 libnsl_hidden_proto (ypbinderr_string)
 libnsl_hidden_proto (yp_bind)
 libnsl_hidden_proto (yp_get_default_domain)
 libnsl_hidden_proto (ypprot_err)
 libnsl_hidden_proto (yp_master)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/rpcsvc/ypupd.h b/include/rpcsvc/ypupd.h
index 7601971..6d179dd 100644
--- a/include/rpcsvc/ypupd.h
+++ b/include/rpcsvc/ypupd.h
@@ -1,8 +1,11 @@
 #ifndef __RPCSVC_YPUPD_H__
 #include <nis/rpcsvc/ypupd.h>

+# ifndef _ISOMAC
+
 libnsl_hidden_proto (xdr_yp_buf)
 libnsl_hidden_proto (xdr_ypdelete_args)
 libnsl_hidden_proto (xdr_ypupdate_args)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/shadow.h b/include/shadow.h
index a3f897c..124a1ab 100644
--- a/include/shadow.h
+++ b/include/shadow.h
@@ -1,6 +1,8 @@
 #ifndef _SHADOW_H
 #include <shadow/shadow.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern int __getspent_r (struct spwd *__result_buf, char *__buffer,
 			 size_t __buflen, struct spwd **__result)
@@ -47,4 +49,5 @@ DECLARE_NSS_PROTOTYPES (nisplus)
 #undef DECLARE_NSS_PROTOTYPES


+# endif /* !_ISOMAC */
 #endif
diff --git a/include/stdio_ext.h b/include/stdio_ext.h
index 354146f..29c6e68 100644
--- a/include/stdio_ext.h
+++ b/include/stdio_ext.h
@@ -1,6 +1,7 @@
 #ifndef	_STDIO_EXT_H
+#include <stdio-common/stdio_ext.h>

-# include <stdio-common/stdio_ext.h>
+# ifndef _ISOMAC

 libc_hidden_proto (__fsetlocking)

@@ -18,5 +19,5 @@ libc_hidden_proto (__fsetlocking)
      __result;								\
   })

-
-#endif
+# endif /* !_ISOMAC */
+#endif /* stdio_ext.h */
diff --git a/include/sys/epoll.h b/include/sys/epoll.h
index ce1c2e2..86e0a54 100644
--- a/include/sys/epoll.h
+++ b/include/sys/epoll.h
@@ -1,6 +1,9 @@
 #ifndef _SYS_EPOLL_H
 #include_next <sys/epoll.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (epoll_pwait)

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/sys/file.h b/include/sys/file.h
index e73a4d1..d0cd1f9 100644
--- a/include/sys/file.h
+++ b/include/sys/file.h
@@ -1,6 +1,10 @@
 #ifndef _SYS_FILE_H
 #include <misc/sys/file.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern int __flock (int __fd, int __operation);
+
+# endif /* !_ISOMAC */
 #endif
diff --git a/include/sys/gmon.h b/include/sys/gmon.h
index 55739cf..30889d8 100644
--- a/include/sys/gmon.h
+++ b/include/sys/gmon.h
@@ -1,6 +1,8 @@
 #ifndef _SYS_GMON_H
 #include <gmon/sys/gmon.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */

 /* Write current profiling data to file.  */
@@ -12,4 +14,6 @@ extern void __bb_init_func (struct __bb *bb);
 extern void __bb_exit_func (void);

 extern struct gmonparam _gmonparam attribute_hidden;
+
+# endif /* !_ISOMAC */
 #endif
diff --git a/include/sys/ioctl.h b/include/sys/ioctl.h
index ebadd52..bfc6909 100644
--- a/include/sys/ioctl.h
+++ b/include/sys/ioctl.h
@@ -1,6 +1,10 @@
 #ifndef _SYS_IOCTL_H
 #include <misc/sys/ioctl.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern int __ioctl (int __fd, unsigned long int __request, ...);
+
+# endif /* !_ISOMAC */
 #endif
diff --git a/include/sys/prctl.h b/include/sys/prctl.h
index 316f454..0920ed6 100644
--- a/include/sys/prctl.h
+++ b/include/sys/prctl.h
@@ -1,6 +1,9 @@
 #ifndef _SYS_PRCTL_H
 #include_next <sys/prctl.h>

+# ifndef _ISOMAC
+
 extern int __prctl (int __option, ...);

+# endif /* !_ISOMAC */
 #endif
diff --git a/include/sys/profil.h b/include/sys/profil.h
index 7bf1700..2b11330 100644
--- a/include/sys/profil.h
+++ b/include/sys/profil.h
@@ -1,9 +1,12 @@
 #ifndef _PROFIL_H
 #include <gmon/sys/profil.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */

 extern int __sprofil (struct prof *__profp, int __profcnt,
 		      struct timeval *__tvp, unsigned int __flags);

+# endif /* !_ISOMAC */
 #endif /* _PROFIL_H */
diff --git a/include/sys/statfs.h b/include/sys/statfs.h
index e34ad02..3fac4a3 100644
--- a/include/sys/statfs.h
+++ b/include/sys/statfs.h
@@ -1,10 +1,14 @@
 #ifndef _SYS_STATFS_H
 #include <io/sys/statfs.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern int __statfs (const char *__file, struct statfs *__buf);
 libc_hidden_proto (__statfs)
 extern int __fstatfs (int __fildes, struct statfs *__buf);
 extern int __statfs64 (const char *__file, struct statfs64 *__buf);
 extern int __fstatfs64 (int __fildes, struct statfs64 *__buf);
+
+# endif /* !_ISOMAC */
 #endif
diff --git a/include/sys/sysctl.h b/include/sys/sysctl.h
index 4fffb4f..2a15e91 100644
--- a/include/sys/sysctl.h
+++ b/include/sys/sysctl.h
@@ -1,10 +1,13 @@
 #ifndef _SYS_SYSCTL_H
 #include_next <sys/sysctl.h>

+# ifndef _ISOMAC
+
 /* Read or write system parameters (Linux, FreeBSD specific).  */
 extern int __sysctl (int *__name, int __nlen, void *__oldval,
 		     size_t *__oldlenp, void *__newval, size_t __newlen);
 libc_hidden_proto (__sysctl)


+# endif /* !_ISOMAC */
 #endif  /* _SYS_SYSCTL_H */
diff --git a/include/sys/sysinfo.h b/include/sys/sysinfo.h
index d33055a..c33eae2 100644
--- a/include/sys/sysinfo.h
+++ b/include/sys/sysinfo.h
@@ -1,6 +1,8 @@
 #ifndef _SYS_SYSINFO_H
 #include_next <sys/sysinfo.h>

+# ifndef _ISOMAC
+
 /* Now we define the internal interface.  */

 /* Return number of configured processors.  */
@@ -18,4 +20,5 @@ extern long int __get_avphys_pages (void);
 /* Return maximum number of processes this real user ID can have.  */
 extern long int __get_child_max (void);

+# endif /* !_ISOMAC */
 #endif /* sys/sysinfo.h */
diff --git a/include/ttyent.h b/include/ttyent.h
index 81e5211..53a6668 100644
--- a/include/ttyent.h
+++ b/include/ttyent.h
@@ -1,5 +1,7 @@
 #ifndef	_TTYENT_H
-# include <misc/ttyent.h>
+#include <misc/ttyent.h>
+
+# ifndef _ISOMAC

 extern __typeof (getttyent) __getttyent __THROW;
 libc_hidden_proto (__getttyent)
@@ -8,4 +10,5 @@ libc_hidden_proto (__setttyent)
 extern __typeof (endttyent) __endttyent __THROW;
 libc_hidden_proto (__endttyent)

-#endif
+# endif /* !_ISOMAC */
+#endif /* ttyent.h */
diff --git a/include/utmp.h b/include/utmp.h
index 28207d1..6b2e262 100644
--- a/include/utmp.h
+++ b/include/utmp.h
@@ -1,6 +1,8 @@
 #ifndef _UTMP_H
 #include <login/utmp.h>

+# ifndef _ISOMAC
+
 /* Now define the internal interfaces.  */
 extern void __updwtmp (const char *__wtmp_file, const struct utmp *__utmp);
 extern int __utmpname (const char *__file);
@@ -18,4 +20,5 @@ extern int __getutline_r (const struct utmp *__line,

 libutil_hidden_proto (login_tty)

+# endif /* !_ISOMAC */
 #endif
diff --git a/scripts/check-installed-headers.sh
b/scripts/check-installed-headers.sh
new file mode 100644
index 0000000..7fbc725
--- /dev/null
+++ b/scripts/check-installed-headers.sh
@@ -0,0 +1,146 @@
+#! /bin/sh
+# Copyright (C) 2016 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+#
+# 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/>.
+
+# Check installed headers for cleanliness.  For each header, confirm
+# that it's possible to compile a file that includes that header and
+# does nothing else, in several different compilation modes.  Also,
+# scan the header for a set of obsolete typedefs that should no longer
+# appear.
+
+# These compilation switches assume GCC or compatible, which is probably
+# fine since we also assume that when _building_ glibc.
+c_modes="-std=c89 -std=gnu89 -std=c11 -std=gnu11"
+cxx_modes="-std=c++98 -std=gnu++98 -std=c++11 -std=gnu++11"
+
+# An exhaustive test of feature selection macros would take far too long.
+# These are probably the most commonly used three.
+lib_modes="-D_DEFAULT_SOURCE=1 -D_GNU_SOURCE=1 -D_XOPEN_SOURCE=700"
+
+# sys/types.h+bits/types.h have to define the obsolete types.
+# rpc(svc)/* have the obsolete types too deeply embedded in their API
+# to remove.
+skip_obsolete_type_check='*/sys/types.h|*/bits/types.h|*/rpc/*|*/rpcsvc/*'
+obsolete_type_re=\
+'\<((__)?(quad_t|u(short|int|long|_(char|short|int([0-9]+_t)?|long|quad_t))))\>'
+
+if [ $# -lt 3 ]; then
+    echo "usage: $0 c|c++ \"compile command\" header header header..." >&2
+    exit 2
+fi
+case "$1" in
+    (c)
+        lang_modes="$c_modes"
+        cih_test_c=$(mktemp ${TMPDIR-/tmp}/cih_test_XXXXXX.c)
+        already="$skip_obsolete_type_check"
+    ;;
+    (c++)
+        lang_modes="$cxx_modes"
+        cih_test_c=$(mktemp ${TMPDIR-/tmp}/cih_test_XXXXXX.cc)
+        # The obsolete-type check can be skipped for C++; it is
+        # sufficient to do it for C.
+        already="*"
+    ;;
+    (*)
+        echo "usage: $0 c|c++ \"compile command\" header header
header..." >&2
+        exit 2;;
+esac
+shift
+cc_cmd="$1"
+shift
+trap "rm -f '$cih_test_c'" 0
+
+failed=0
+is_x86_64=unknown
+for header in "$@"; do
+    # Skip various headers for which this test gets a false failure.
+    case "$header" in
+        # bits/* are not meant to be included directly and usually #error
+        # out if you try it.
+        # regexp.h is a stub containing only an #error.
+        # Sun RPC's .x files are traditionally installed in
+        # $prefix/include/rpcsvc, but they are not C header files.
+        (bits/* | regexp.h | rpcsvc/*.x)
+            continue;;
+
+        # sys/elf.h and sys/vm86.h are "unsupported on x86-64" and
+        # #error out on that target.
+        (sys/elf.h | sys/vm86.h)
+            case "$is_x86_64" in
+                (yes) continue;;
+                (no)  ;;
+                (unknown)
+                    cat >"$cih_test_c" <<EOF
+#if defined __x86_64__ && __x86_64__
+#error "is x86-64"
+#endif
+EOF
+                    if $cc_cmd -fsyntax-only "$cih_test_c" > /dev/null 2>&1
+                    then
+                        is_x86_64=no
+                    else
+                        is_x86_64=yes
+                        continue
+                    fi
+                ;;
+            esac
+    esac
+
+    echo :: "$header"
+    for lang_mode in "" $lang_modes; do
+        for lib_mode in "" $lib_modes; do
+            echo :::: $lang_mode $lib_mode
+            if [ -z "$lib_mode" ]; then
+                expanded_lib_mode='/* default library mode */'
+            else
+                expanded_lib_mode=$(echo : $lib_mode | \
+                    sed 's/^: -D/#define /; s/=/ /')
+            fi
+            cat >"$cih_test_c" <<EOF
+/* These macros may have been defined on the command line.  They are
+   inappropriate for this test.  */
+#undef _LIBC
+#undef _GNU_SOURCE
+#undef _REENTRANT
+/* The library mode is selected here rather than on the command line to
+   ensure that this selection wins. */
+$expanded_lib_mode
+#include <$header>
+int avoid_empty_translation_unit;
+EOF
+            if $cc_cmd -fsyntax-only $lang_mode "$cih_test_c" 2>&1
+            then
+                includes=$($cc_cmd -fsyntax-only -H $lang_mode \
+                              "$cih_test_c" 2>&1 | sed -ne 's/^[.][.]*
//p')
+                for h in $includes; do
+                    # Don't repeat work.
+                    eval 'case "$h" in ('"$already"') continue;; esac'
+
+                    if grep -qE "$obsolete_type_re" "$h"; then
+                        echo "*** Obsolete types detected:"
+                        grep -HE "$obsolete_type_re" "$h"
+                        failed=1
+                    fi
+                    already="$already|$h"
+                done
+            else
+                failed=1
+            fi
+        done
+    done
+done
+exit $failed
diff --git a/sysdeps/arm/nacl/include/bits/setjmp.h
b/sysdeps/arm/nacl/include/bits/setjmp.h
index 6b6a235..e1fe505 100644
--- a/sysdeps/arm/nacl/include/bits/setjmp.h
+++ b/sysdeps/arm/nacl/include/bits/setjmp.h
@@ -24,6 +24,8 @@
 # include <sysdeps/arm/bits/setjmp.h>
 #endif

+# ifndef _ISOMAC
+
 /* Register list for a ldm/stm instruction to load/store
    the general registers from a __jmp_buf.

@@ -35,4 +37,5 @@
 /* Index of __jmp_buf where the sp register resides.  */
 #define __JMP_BUF_SP		0

+# endif /* _ISOMAC */
 #endif  /* include/bits/setjmp.h */
diff --git a/sysdeps/mips/include/sys/asm.h b/sysdeps/mips/include/sys/asm.h
index 7e288df..67acf74 100644
--- a/sysdeps/mips/include/sys/asm.h
+++ b/sysdeps/mips/include/sys/asm.h
@@ -16,8 +16,9 @@
    <http://www.gnu.org/licenses/>.  */

 #ifndef _SYS_ASM_H
+#include_next <sys/asm.h>

-# include_next <sys/asm.h>
+# ifndef _ISOMAC

 # undef __mips_cfi_startproc
 # define __mips_cfi_startproc cfi_startproc
@@ -50,4 +51,5 @@
 	cfi_restore (gp)
 # endif

-#endif
+# endif /* _ISOMAC */
+#endif /* sys/asm.h */
diff --git a/sysdeps/unix/sysv/linux/include/sys/sysinfo.h
b/sysdeps/unix/sysv/linux/include/sys/sysinfo.h
index 50077fb..b76f7e0 100644
--- a/sysdeps/unix/sysv/linux/include/sys/sysinfo.h
+++ b/sysdeps/unix/sysv/linux/include/sys/sysinfo.h
@@ -21,6 +21,9 @@

 #include_next <sys/sysinfo.h>

+# ifndef _ISOMAC
+
 extern __typeof (sysinfo) __sysinfo __THROW;

+# endif /* _ISOMAC */
 #endif /* sys/sysinfo.h */
diff --git a/sysdeps/unix/sysv/linux/include/sys/timex.h
b/sysdeps/unix/sysv/linux/include/sys/timex.h
index ace90ee..4b4ff88 100644
--- a/sysdeps/unix/sysv/linux/include/sys/timex.h
+++ b/sysdeps/unix/sysv/linux/include/sys/timex.h
@@ -21,6 +21,9 @@

 #include_next <sys/timex.h>

+# ifndef _ISOMAC
+
 libc_hidden_proto (__adjtimex)

+# endif /* _ISOMAC */
 #endif /* sys/timex.h */
diff --git a/sysdeps/x86/fpu/include/bits/fenv.h
b/sysdeps/x86/fpu/include/bits/fenv.h
index 6e8b733..a410ed0 100644
--- a/sysdeps/x86/fpu/include/bits/fenv.h
+++ b/sysdeps/x86/fpu/include/bits/fenv.h
@@ -16,8 +16,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */

+#ifndef _BITS_FENV_H
 #include_next <bits/fenv.h>

+# ifndef _ISOMAC
+
 /* Ensure __feraiseexcept calls in glibc are optimized the same as
    feraiseexcept calls.  */

@@ -40,3 +43,6 @@ __NTH (__feraiseexcept (int __excepts))

 __END_DECLS
 #endif
+
+# endif /* _ISOMAC */
+#endif /* bits/fenv.h */
