diff -r 4b6e6a77e501 Modules/clinic/posixmodule.c.h
--- a/Modules/clinic/posixmodule.c.h	Sat Oct 22 03:21:55 2016 +0000
+++ b/Modules/clinic/posixmodule.c.h	Sat Oct 22 07:19:27 2016 +0200
@@ -1411,6 +1411,8 @@
 
 #endif /* defined(HAVE_SYSTEM) && !defined(MS_WINDOWS) */
 
+#if (defined(MS_WINDOWS) || defined(HAVE_UMASK))
+
 PyDoc_STRVAR(os_umask__doc__,
 "umask($module, mask, /)\n"
 "--\n"
@@ -1438,6 +1440,8 @@
     return return_value;
 }
 
+#endif /* (defined(MS_WINDOWS) || defined(HAVE_UMASK)) */
+
 PyDoc_STRVAR(os_unlink__doc__,
 "unlink($module, /, path, *, dir_fd=None)\n"
 "--\n"
@@ -5757,6 +5761,10 @@
     #define OS_SYSTEM_METHODDEF
 #endif /* !defined(OS_SYSTEM_METHODDEF) */
 
+#ifndef OS_UMASK_METHODDEF
+    #define OS_UMASK_METHODDEF
+#endif /* !defined(OS_UMASK_METHODDEF) */
+
 #ifndef OS_UNAME_METHODDEF
     #define OS_UNAME_METHODDEF
 #endif /* !defined(OS_UNAME_METHODDEF) */
diff -r 4b6e6a77e501 Modules/posixmodule.c
--- a/Modules/posixmodule.c	Sat Oct 22 03:21:55 2016 +0000
+++ b/Modules/posixmodule.c	Sat Oct 22 07:19:27 2016 +0200
@@ -4141,6 +4141,7 @@
 #endif /* HAVE_SYSTEM */
 
 
+#if defined(MS_WINDOWS) || defined(HAVE_UMASK)
 /*[clinic input]
 os.umask
 
@@ -4159,6 +4160,7 @@
         return posix_error();
     return PyLong_FromLong((long)i);
 }
+#endif /* MS_WINDOWS || HAVE_UMASK */
 
 #ifdef MS_WINDOWS
 
diff -r 4b6e6a77e501 configure.ac
--- a/configure.ac	Sat Oct 22 03:21:55 2016 +0000
+++ b/configure.ac	Sat Oct 22 07:19:27 2016 +0200
@@ -3422,8 +3422,8 @@
  sigaction sigaltstack siginterrupt sigpending sigrelse \
  sigtimedwait sigwait sigwaitinfo snprintf strftime strlcpy symlinkat sync \
  sysconf tcgetpgrp tcsetpgrp tempnam timegm times tmpfile tmpnam tmpnam_r \
- truncate uname unlinkat unsetenv utimensat utimes waitid waitpid wait3 wait4 \
- wcscoll wcsftime wcsxfrm wmemcmp writev _getpty)
+ truncate umask uname unlinkat unsetenv utimensat utimes waitid waitpid wait3 \
+ wait4 wcscoll wcsftime wcsxfrm wmemcmp writev _getpty)
 
 AC_CHECK_DECL(dirfd,
     AC_DEFINE(HAVE_DIRFD, 1,