diff --git a/Lib/multiprocessing/util.py b/Lib/multiprocessing/util.py
index 207a2f7..3e640b9 100644
--- a/Lib/multiprocessing/util.py
+++ b/Lib/multiprocessing/util.py
@@ -429,7 +429,7 @@
         return _posixsubprocess.fork_exec(
             args, [os.fsencode(path)], True, passfds, None, None,
             -1, -1, -1, -1, -1, -1, errpipe_read, errpipe_write,
-            False, False, None, None, None, None)
+            False, False, None, None, None, -1, None)
     finally:
         os.close(errpipe_read)
         os.close(errpipe_write)
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 1016874..b5a45d9 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -733,6 +733,8 @@
 
       user (POSIX only)
 
+      umask (POSIX only)
+
       pass_fds (POSIX only)
 
       encoding and errors: Text mode encoding and error handling to use for
@@ -750,7 +752,7 @@
                  startupinfo=None, creationflags=0,
                  restore_signals=True, start_new_session=False,
                  pass_fds=(), *, user=None, group=None, extra_groups=None,
-                 encoding=None, errors=None, text=None):
+                 encoding=None, errors=None, text=None, umask=-1):
         """Create new Popen instance."""
         _cleanup()
         # Held while anything is calling waitpid before returncode has been
@@ -945,7 +947,7 @@
                                 c2pread, c2pwrite,
                                 errread, errwrite,
                                 restore_signals,
-                                gid, gids, uid,
+                                gid, gids, uid, umask,
                                 start_new_session)
         except:
             # Cleanup if the child failed starting.
@@ -1318,6 +1320,7 @@
                            errread, errwrite,
                            unused_restore_signals,
                            unused_gid, unused_gids, unused_uid,
+                           unused_umask,
                            unused_start_new_session):
             """Execute program (MS Windows version)"""
 
@@ -1645,7 +1648,7 @@
                            c2pread, c2pwrite,
                            errread, errwrite,
                            restore_signals,
-                           gid, gids, uid,
+                           gid, gids, uid, umask,
                            start_new_session):
             """Execute program (POSIX version)"""
 
@@ -1684,7 +1687,8 @@
                     and not start_new_session
                     and gid is None
                     and gids is None
-                    and uid is None):
+                    and uid is None
+                    and umask < 0):
                 self._posix_spawn(args, executable, env, restore_signals,
                                   p2cread, p2cwrite,
                                   c2pread, c2pwrite,
@@ -1738,7 +1742,7 @@
                             errread, errwrite,
                             errpipe_read, errpipe_write,
                             restore_signals, start_new_session,
-                            gid, gids, uid,
+                            gid, gids, uid, umask,
                             preexec_fn)
                     self._child_created = True
                 finally:
diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index 6731447..2024435 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -97,7 +97,7 @@
             def __len__(self):
                 return 1
         self.assertRaises(TypeError, _posixsubprocess.fork_exec,
-                          1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20)
+                          1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21)
         # Issue #15736: overflow in _PySequence_BytesToCharpArray()
         class Z(object):
             def __len__(self):
@@ -105,7 +105,7 @@
             def __getitem__(self, i):
                 return b'x'
         self.assertRaises(MemoryError, _posixsubprocess.fork_exec,
-                          1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20)
+                          1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21)
 
     @unittest.skipUnless(_posixsubprocess, '_posixsubprocess required for this test.')
     def test_subprocess_fork_exec(self):
@@ -115,7 +115,7 @@
 
         # Issue #15738: crash in subprocess_fork_exec()
         self.assertRaises(TypeError, _posixsubprocess.fork_exec,
-                          Z(),[b'1'],3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20)
+                          Z(),[b'1'],3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21)
 
     @unittest.skipIf(MISSING_C_DOCSTRINGS,
                      "Signature information for builtins requires docstrings")
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 2251640..5cc324b 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1894,6 +1894,28 @@
         with self.assertRaises(ValueError):
             subprocess.check_call([sys.executable, "-c", "pass"], extra_groups=[])
 
+    @unittest.skipIf(mswindows or not hasattr(os, 'umask'),
+                     'POSIX umask() is not available.')
+    def test_umask(self):
+        tmpdir = None
+        try:
+            tmpdir = tempfile.mkdtemp()
+            name = os.path.join(tmpdir, "beans")
+            # We set an unusual umask in the child so as a unique mode
+            # for us to test the child's touched file for.
+            subprocess.check_call(
+                    [sys.executable, "-c", f"open({name!r}, 'w')"],  # touch
+                    umask=0o053)
+            # Ignore execute permissions entirely in our test,
+            # filesystems could be mounted to ignore or force that.
+            st_mode = os.stat(name).st_mode & 0o666
+            expected_mode = 0o624
+            self.assertEqual(expected_mode, st_mode,
+                             msg=f'{oct(expected_mode)} != {oct(st_mode)}')
+        finally:
+            if tmpdir is not None:
+                shutil.rmtree(tmpdir)
+
     def test_run_abort(self):
         # returncode handles signal termination
         with support.SuppressCrashReport():
@@ -2950,7 +2972,7 @@
                         -1, -1, -1, -1,
                         1, 2, 3, 4,
                         True, True,
-                        False, [], 0,
+                        False, [], 0, -1,
                         func)
                 # Attempt to prevent
                 # "TypeError: fork_exec() takes exactly N arguments (M given)"
@@ -2999,7 +3021,7 @@
                         -1, -1, -1, -1,
                         1, 2, 3, 4,
                         True, True,
-                        None, None, None,
+                        None, None, None, -1,
                         None)
                 self.assertIn('fds_to_keep', str(c.exception))
         finally: