diff --git a/src/pylib/Lib/os.nim b/src/pylib/Lib/os.nim
index e5c9a8732..3bf07511d 100644
--- a/src/pylib/Lib/os.nim
+++ b/src/pylib/Lib/os.nim
@@ -8,9 +8,9 @@ export os
 
 import ./os_impl/[
   consts, posix_like, subp, utils, path, walkImpl, listdirx,
-  term]
+  term, inheritable]
 export
   consts, posix_like, subp, utils, path, walkImpl, listdirx,
-  term
+  term, set_inheritable, get_inheritable
 
 
diff --git a/src/pylib/Lib/os_impl/inheritable.nim b/src/pylib/Lib/os_impl/inheritable.nim
new file mode 100644
index 000000000..eb4cbd285
--- /dev/null
+++ b/src/pylib/Lib/os_impl/inheritable.nim
@@ -0,0 +1,182 @@
+
+
+import ../../pyerrors/oserr
+
+const
+  MS_WINDOWS = defined(windows)
+  SupportIoctlInheritCtl = (defined(linux) or defined(bsd)) and
+                              not defined(nimscript)
+  # XXX: hard to express as following in Nim
+  # defined(HAVE_SYS_IOCTL_H) && defined(FIOCLEX) && defined(FIONCLEX)
+
+when MS_WINDOWS:
+  import std/winlean
+else:
+  import std/posix
+  when SupportIoctlInheritCtl:
+    {.push header: "<sys/ioctl.h>".}
+    let FIOCLEX{.importc.}: uint
+    let FIONCLEX{.importc.}: uint
+    {.pop.}
+
+when MS_WINDOWS:
+  template with_Py_SUPPRESS_IPH(body) = body # TODO
+
+  proc Py_get_osfhandle_noraise(fd: int): Handle =
+    with_Py_SUPPRESS_IPH:
+      result = get_osfhandle FileHandle fd
+else:
+  template with_Py_SUPPRESS_IPH(body) = body
+
+# === get_inheritable ===
+
+template ifRaiseThenErrnoOrN1 =
+  if ifRaise:
+    raiseErrno()
+  return -1
+
+template ifRaiseThenWinErr0OrN1 =
+  static: assert MS_WINDOWS
+  if ifRaise:
+    # in Windows, raiseOSError raises Windows Error
+    raiseOSError OSErrorCode 0
+  return -1
+
+proc get_inheritable(fd: int, ifRaise: bool): int =
+  when MS_WINDOWS:
+    let handle = Py_get_osfhandle_noraise fd
+    if handle == INVALID_HANDLE_VALUE:
+      ifRaiseThenErrnoOrN1
+    var flags: DWORD
+    if not bool getHandleInformation(handle, flags.addr):
+      ifRaiseThenWinErr0OrN1
+    return flags.int and HANDLE_FLAG_INHERIT.int
+  else:
+    let flags = fcntl(fd.cint, F_GETFD)
+    if flags == -1:
+      ifRaiseThenErrnoOrN1
+    return int(not bool(flags and FD_CLOEXEC))
+
+proc get_inheritable*(fd: int): bool =
+  with_Py_SUPPRESS_IPH:
+    result = bool get_inheritable(fd, true)
+    # as ifRaise == true, the returned value cannot be -1,
+    # but raise Exception on error
+
+# === set_inheritable ===
+
+# works fine on Windows
+{.emit:"""/*VARSECTION*/
+static const int _defined_O_PATH =
+#if defined(O_PATH)
+  1
+#else
+  0
+#endif
+; // defined shall only occur after #if/#elif
+""".}
+
+let
+  c_defined_O_PATH{.importc: "_defined_O_PATH", nodecl.}: cint
+  defined_O_PATH = bool c_defined_O_PATH
+
+
+#import std/sysatomics # already export by system
+
+proc Py_atomic_load_relaxed[T](obj: ptr T): T =
+  atomicLoadN obj, ATOMIC_RELAXED
+proc Py_atomic_store_relaxed[T](obj: ptr T, value: T) =
+  atomicStoreN obj, value, ATOMIC_RELAXED
+
+proc set_inheritable(fd: int, inheritable: bool, ifRaise: bool, atomic_flag_works: ptr int): int =
+  ##[ there are setInheritable in std/syncio,
+   which, however:
+    - accept Handle which still need get_osfhandle/fcntl to get from `fd`
+    - don't try "fast-path" and try fallback
+    - don't respect what we do in `block check_errno`
+  ]##
+  # atomic_flag_works can only be used to make the file descriptor
+  #     non-inheritable
+  let atomic_fw_nNil = not atomic_flag_works.isNil
+  assert not (atomic_fw_nNil and inheritable)
+  if atomic_fw_nNil and not inheritable:
+    if atomic_flag_works[] == -1:
+      let isInheritable = get_inheritable(fd, ifRaise)
+      if isInheritable == -1:
+        return -1
+      atomic_flag_works[] = int bool isInheritable
+    
+    if bool atomic_flag_works[]:
+      return 0
+  when MS_WINDOWS:
+    let handle = Py_get_osfhandle_noraise FileHandle fd
+    if handle == INVALID_HANDLE_VALUE:
+      ifRaiseThenErrnoOrN1
+    let flags = DWORD:
+      if inheritable: HANDLE_FLAG_INHERIT else: 0
+    if not bool setHandleInformation(handle, HANDLE_FLAG_INHERIT, flags):
+      ifRaiseThenWinErr0OrN1
+    return 0
+  else:
+    let fd = cint fd
+    when SupportIoctlInheritCtl:
+      var ioctl_works{.global.} = -1
+      if ifRaise and Py_atomic_load_relaxed(ioctl_works.addr) != 0:
+        # fast-path: ioctl() only requires one syscall
+        #[ caveat: raise=0 is an indicator that we must be async-signal-safe
+           thus avoid using ioctl() so we skip the fast-path. ]#
+        let requested =
+          if inheritable: FIONCLEX
+          else: FIOCLEX
+        let err = ioctl(fd, requested, nil)
+        if err == 0:
+          if Py_atomic_load_relaxed(ioctl_works.addr) == -1:
+            Py_atomic_store_relaxed(ioctl_works.addr, 1)
+          return 0
+
+        block check_errno:
+          if errno != ENOTTY and errno != EACCES:
+            if defined_O_PATH:
+              if errno == EBADF:
+                #[bpo-44849: On Linux and FreeBSD, ioctl(FIOCLEX) fails with EBADF
+                  on O_PATH file descriptors. Fall through to the fcntl()
+                  implementation.  ]#
+                break check_errno
+            ifRaiseThenErrnoOrN1
+          else:
+            #[Issue #22258: Here, ENOTTY means "Inappropriate ioctl for
+              device". The ioctl is declared but not supported by the kernel.
+              Remember that ioctl() doesn't work. It is the case on
+              Illumos-based OS for example.
+
+              Issue #27057: When SELinux policy disallows ioctl it will fail
+              with EACCES. While FIOCLEX is safe operation it may be
+              unavailable because ioctl was denied altogether.
+              This can be the case on Android.]#
+            Py_atomic_store_relaxed(ioctl_works.addr, 0)
+          # fallback to fcntl() if ioctl() does not work
+    # low-path: fcntl() requires two syscalls
+    let flags = fcntl(fd, F_GETFD)
+    if flags < 0:
+      ifRaiseThenErrnoOrN1
+    let new_flags =
+      if inheritable: flags and not FD_CLOEXEC
+      else: flags or FD_CLOEXEC
+    if new_flags == flags:
+      # FD_CLOEXEC flag already set/cleared: nothing to do
+      return 0
+    let res = fcntl(fd, F_SETFD, new_flags)
+    if res < 0:
+      ifRaiseThenErrnoOrN1
+    return 0
+
+proc Py_set_inheritable*(fd: int, inheritable: bool, atomic_flag_works: ptr int): int =
+  # used by socket, etc
+  set_inheritable(fd, inheritable, true, atomic_flag_works)
+
+proc set_inheritableImpl*(fd: int; inheritable: bool) =
+  with_Py_SUPPRESS_IPH:
+    discard Py_set_inheritable(fd, inheritable, nil)
+
+proc set_inheritable*(fd: int; inheritable: int|bool) =
+  set_inheritableImpl(fd, bool inheritable)
diff --git a/src/pylib/Lib/test/test_os.nim b/src/pylib/Lib/test/test_os.nim
index 13001df72..39b11aa1c 100644
--- a/src/pylib/Lib/test/test_os.nim
+++ b/src/pylib/Lib/test/test_os.nim
@@ -2,29 +2,39 @@
 import ./import_utils
 importTestPyLib os
 
-test "Lib/os":
+suite "Lib/os":
   const fn = "tempfiletest"
-  template open(fd: int, s: string): untyped{.used.} =  # this won't be called
-    doAssert false
-    io.open(fd, s)
-  let fd = open(fn, O_RDWR|O_CREAT)
-  var f = fdopen(fd, "w+")
-  let s = "123"
-  f.write(s)
-  f.seek(0)
-  let res = f.read()
-  f.close()
-  check res == s
+  test "open fdopen close":
+    
+    template open(fd: int, s: string): untyped{.used.} =  # this won't be called
+      doAssert false
+      io.open(fd, s)
+    let fd = open(fn, O_RDWR|O_CREAT)
+    var f = fdopen(fd, "w+")
+    let s = "123"
+    f.write(s)
+    f.seek(0)
+    let res = f.read()
+    f.close()
+    check res == s
+  test "mkdir rmdir":
+    const invalidDir = "No one will name such a dir"
+    checkpoint "rmdir"
+    expect FileNotFoundError:
+      os.rmdir(invalidDir)
 
-  const invalidDir = "No one will name such a dir"
-  checkpoint "rmdir"
-  expect FileNotFoundError:
-    os.rmdir(invalidDir)
+    checkpoint "mkdir"
+    expect FileNotFoundError:
+      # parent dir is not found
+      os.mkdir(invalidDir + os.sep + "non-file")
 
-  checkpoint "mkdir"
-  expect FileNotFoundError:
-    # parent dir is not found
-    os.mkdir(invalidDir + os.sep + "non-file")
+  test "get,set_inheritable":
+    let fd = os.open(fn, os.O_RDONLY)
+    defer: os.close(fd)
+    check not os.get_inheritable(fd)
+
+    os.set_inheritable(fd, True)
+    check os.get_inheritable(fd)
 
 test "os.path":
   ## only test if os.path is correctly export