diff --git a/libgo/go/net/fd_unix.go b/libgo/go/net/fd_unix.go
index 9ed4f753649..4911ab0abe3 100644
--- a/libgo/go/net/fd_unix.go
+++ b/libgo/go/net/fd_unix.go
@@ -410,7 +410,7 @@ func (fd *netFD) accept(toAddr func(syscall.Sockaddr) Addr) (netfd *netFD, err e
 var tryDupCloexec = int32(1)
 
 func dupCloseOnExec(fd int) (newfd int, err error) {
-	if atomic.LoadInt32(&tryDupCloexec) == 1 {
+	if atomic.LoadInt32(&tryDupCloexec) == 1 && syscall.F_DUPFD_CLOEXEC != 0 {
 		r0, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_DUPFD_CLOEXEC, 0)
 		if runtime.GOOS == "darwin" && e1 == syscall.EBADF {
 			// On OS X 10.6 and below (but we only support
diff --git a/libgo/mksysinfo.sh b/libgo/mksysinfo.sh
index a1713df9b57..025729ccad1 100755
--- a/libgo/mksysinfo.sh
+++ b/libgo/mksysinfo.sh
@@ -220,6 +220,11 @@ if ! grep '^const O_CLOEXEC' ${OUT} >/dev/null 2>&1; then
   echo "const O_CLOEXEC = 0" >> ${OUT}
 fi
 
+# The os package requires F_DUPFD_CLOEXEC to be defined.
+if ! grep '^const F_DUPFD_CLOEXEC' ${OUT} >/dev/null 2>&1; then
+  echo "const F_DUPFD_CLOEXEC = 0" >> ${OUT}
+fi
+
 # These flags can be lost on i386 GNU/Linux when using
 # -D_FILE_OFFSET_BITS=64, because we see "#define F_SETLK F_SETLK64"
 # before we see the definition of F_SETLK64.