--- blink/blinkenlights.c
+++ blink/blinkenlights.c
@@ -3559,9 +3559,11 @@ static void GetOpts(int argc, char *argv[]) {
   FLAG_nolinear = !wantunsafe;
 }
 
+#ifdef HAVE_JIT
 static void AddPath_StartOp_Tui(P) {
   Jitter(m, rde, 0, 0, "qc", StartOp_Tui);
 }
+#endif
 
 static bool FileExists(const char *path) {
   return !VfsAccess(AT_FDCWD, path, F_OK, 0);
@@ -3606,7 +3608,7 @@ int VirtualMachine(int argc, char *argv[]) {
         tty = VfsOpen(AT_FDCWD, "/dev/tty", O_RDWR | O_NOCTTY, 0);
       }
       if (tty != -1) {
-        tty = VfsFcntl(tty, F_DUPFD_CLOEXEC, kMinBlinkFd);
+        tty = VfsFcntl(tty, F_DUPFD, kMinBlinkFd);
       }
       if (tty == -1) {
         WriteErrorString("failed to open /dev/tty\n");
--- blink/demangle.c
+++ blink/demangle.c
@@ -139,10 +139,20 @@ static void SpawnCxxFilt(void) {
   }
   unassert(!close(pipefds[0][1]));
   unassert(!close(pipefds[1][0]));
+#ifndef F_DUPFD_CLOEXEC
+  g_cxxfilt.reader = fcntl(pipefds[0][0], F_DUPFD, kMinBlinkFd);
+  fcntl(g_cxxfilt.reader, F_SETFD, FD_CLOEXEC);
+#else
   g_cxxfilt.reader = fcntl(pipefds[0][0], F_DUPFD_CLOEXEC, kMinBlinkFd);
+#endif
   unassert(g_cxxfilt.reader != -1);
   unassert(!close(pipefds[0][0]));
+#ifndef F_DUPFD_CLOEXEC
+  g_cxxfilt.writer = fcntl(pipefds[1][1], F_DUPFD, kMinBlinkFd);
+  fcntl(g_cxxfilt.writer, F_SETFD, FD_CLOEXEC);
+#else
   g_cxxfilt.writer = fcntl(pipefds[1][1], F_DUPFD_CLOEXEC, kMinBlinkFd);
+#endif
   unassert(g_cxxfilt.writer != -1);
   unassert(!close(pipefds[1][1]));
   unassert(!atexit(CloseCxxFilt));
--- blink/errfd.c
+++ blink/errfd.c
@@ -48,6 +48,11 @@ int WriteError(int fd, const char *buf, int len) {
 
 void WriteErrorInit(void) {
   if (g_errfd) return;
+#ifndef F_DUPFD_CLOEXEC
+  g_errfd = fcntl(2, F_DUPFD, kMinBlinkFd);
+  fcntl(g_errfd, F_SETFD, FD_CLOEXEC);
+#else
   g_errfd = fcntl(2, F_DUPFD_CLOEXEC, kMinBlinkFd);
+#endif
   if (g_errfd == -1) exit(200);
 }
--- blink/log.c
+++ blink/log.c
@@ -120,7 +120,12 @@ static void OpenLog(void) {
       return;
     }
   }
+#ifndef F_DUPFD_CLOEXEC
+  unassert((g_log.fd = fcntl(fd, F_DUPFD, kMinBlinkFd)) != -1);
+  unassert(fcntl(g_log.fd, F_SETFL, FD_CLOEXEC) != -1);
+#else
   unassert((g_log.fd = fcntl(fd, F_DUPFD_CLOEXEC, kMinBlinkFd)) != -1);
+#endif
   unassert(!close(fd));
 }
 
--- blink/path.c
+++ blink/path.c
@@ -156,7 +156,7 @@ void(SetupCod)(struct Machine *m) {
   DisLoadElf(&g_dis, &m->system->elf);
   g_cod = VfsOpen(AT_FDCWD_LINUX, "/tmp/blink.s",
                   O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
-  g_cod = VfsFcntl(g_cod, F_DUPFD_CLOEXEC, kMinBlinkFd);
+  g_cod = VfsFcntl(g_cod, F_DUPFD, kMinBlinkFd);
 #endif
 }
 
--- blink/syscall.c
+++ blink/syscall.c
@@ -1409,8 +1409,18 @@ static int SysDup3(struct Machine *m, i32 fildes, i32 newfildes, i32 flags) {
 static int SysDupf(struct Machine *m, i32 fildes, i32 minfildes, int cmd) {
   struct Fd *fd;
   int lim, oflags, newfildes;
+  int cmdnative = cmd;
   if (minfildes >= (lim = GetFileDescriptorLimit(m->system))) return emfile();
-  if ((newfildes = VfsFcntl(fildes, cmd, minfildes)) != -1) {
+  if (cmd == F_DUPFD_LINUX) {
+    cmdnative = F_DUPFD;
+  } else if (cmd == F_DUPFD_CLOEXEC_LINUX) {
+#ifndef F_DUPFD_CLOEXEC
+    cmdnative = F_DUPFD;
+#else
+    cmdnative = F_DUPFD_CLOEXEC;
+#endif
+  }
+  if ((newfildes = VfsFcntl(fildes, cmdnative, minfildes)) != -1) {
     if (newfildes >= lim) {
       VfsClose(newfildes);
       return emfile();
@@ -1418,7 +1428,7 @@ static int SysDupf(struct Machine *m, i32 fildes, i32 minfildes, int cmd) {
     LOCK(&m->system->fds.lock);
     unassert(fd = GetFd(&m->system->fds, fildes));
     oflags = fd->oflags & ~O_CLOEXEC;
-    if (cmd == F_DUPFD_CLOEXEC) {
+    if (cmd == F_DUPFD_CLOEXEC_LINUX) {
       oflags |= O_CLOEXEC;
     }
     unassert(ForkFd(&m->system->fds, fd, newfildes, oflags));
@@ -3241,10 +3251,8 @@ static int SysFcntlGetownEx(struct Machine *m, i32 fildes, i64 addr) {
 static int SysFcntl(struct Machine *m, i32 fildes, i32 cmd, i64 arg) {
   int rc, fl;
   struct Fd *fd;
-  if (cmd == F_DUPFD_LINUX) {
-    return SysDupf(m, fildes, arg, F_DUPFD);
-  } else if (cmd == F_DUPFD_CLOEXEC_LINUX) {
-    return SysDupf(m, fildes, arg, F_DUPFD_CLOEXEC);
+  if (cmd == F_DUPFD_LINUX || cmd == F_DUPFD_CLOEXEC_LINUX) {
+    return SysDupf(m, fildes, arg, cmd);
   }
   if (!(fd = GetAndLockFd(m, fildes))) return -1;
   if (cmd == F_GETFD_LINUX) {
--- blink/vfs.c
+++ blink/vfs.c
@@ -1733,7 +1733,11 @@ int VfsFcntl(int fd, int cmd, ...) {
   }
   va_start(ap, cmd);
   // CLOEXEC is already handled by the syscall layer.
+#ifndef F_DUPFD_CLOEXEC
+  if (cmd == F_DUPFD) {
+#else
   if (cmd == F_DUPFD || cmd == F_DUPFD_CLOEXEC) {
+#endif
     if (info->device->ops->Dup) {
       ret = info->device->ops->Dup(info, &newinfo);
       if (ret != -1) {
--- blink/xlat.h
+++ blink/xlat.h
@@ -8,6 +8,7 @@
 #include <sys/stat.h>
 #include <sys/statvfs.h>
 #include <sys/time.h>
+#include <sys/types.h>
 #include <termios.h>
 
 #include "blink/linux.h"
--- configure
+++ configure
@@ -295,12 +295,12 @@ replace() {
 
 comment() {
   hassstr "$1"
-  replace "$1" "// $1"
+  replace "$1\$" "// $1"
 }
 
 uncomment() {
   hassstr "$1"
-  replace "// $1" "$1"
+  replace "// $1\$" "$1"
 }
 
 for x; do