diff --git a/configure.in b/configure.in
index 2dc0c94c8..3a7e7aae0 100644
--- a/configure.in
+++ b/configure.in
@@ -534,7 +534,10 @@ AC_HEADER_DIRENT
 AC_HEADER_TIME
 AC_HEADER_SYS_WAIT
 
-AC_CHECK_HEADERS([io.h libc.h limits.h malloc.h memory.h string.h \
+# Reasons for testing:
+#   fenv.h - available in C99, but not older systems
+#
+AC_CHECK_HEADERS([fenv.h io.h libc.h limits.h malloc.h memory.h string.h \
 regex.h rxposix.h rx/rxposix.h sys/dir.h sys/ioctl.h sys/select.h \
 sys/time.h sys/timeb.h sys/times.h sys/stdtypes.h sys/types.h \
 sys/utime.h time.h unistd.h utime.h pwd.h grp.h sys/utsname.h \
@@ -598,12 +601,13 @@ AC_CHECK_HEADERS([assert.h crt_externs.h])
 #   DINFINITY - OSF specific
 #   DQNAN - OSF specific
 #       (DINFINITY and DQNAN are actually global variables, not functions)
+#   fesetround - available in C99, but not older systems
 #   gmtime_r - recent posix, not on old systems
 #   readdir_r - recent posix, not on old systems
 #   sysconf - not on old systems
 #   _NSGetEnviron - Darwin specific
 #
-AC_CHECK_FUNCS([DINFINITY DQNAN ctermid ftime fchown getcwd geteuid gettimeofday gmtime_r lstat mkdir mknod nice readdir_r readlink rename rmdir select setegid seteuid setlocale setpgid setsid sigaction siginterrupt strftime strptime symlink sync sysconf tcgetpgrp tcsetpgrp times uname waitpid strdup system usleep atexit on_exit chown link fcntl ttyname getpwent getgrent kill getppid getpgrp fork setitimer getitimer strchr strcmp index bcopy memcpy rindex unsetenv _NSGetEnviron])
+AC_CHECK_FUNCS([DINFINITY DQNAN ctermid fesetround ftime fchown getcwd geteuid gettimeofday gmtime_r lstat mkdir mknod nice readdir_r readlink rename rmdir select setegid seteuid setlocale setpgid setsid sigaction siginterrupt strftime strptime symlink sync sysconf tcgetpgrp tcsetpgrp times uname waitpid strdup system usleep atexit on_exit chown link fcntl ttyname getpwent getgrent kill getppid getpgrp fork setitimer getitimer strchr strcmp index bcopy memcpy rindex unsetenv _NSGetEnviron])
 
 # Reasons for testing:
 #   netdb.h - not in mingw