Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(revision 88680)
+++ Modules/posixmodule.c	(working copy)
@@ -2929,6 +2929,7 @@
     PyObject *opath;
     char *path;
     int mode = 0777;
+    int mask;
 
 #ifdef MS_WINDOWS
     PyUnicodeObject *po;
@@ -2974,6 +2975,11 @@
     res = mkdir(path);
 #else
     res = mkdir(path, mode);
+    if (res == 0) {
+        mask = umask(0);
+        umask(mask);
+        res = chmod(path, mode ^ mask);
+    }
 #endif
     Py_END_ALLOW_THREADS
     if (res < 0)
@@ -8314,6 +8320,7 @@
     PyObject *opath;
     char *path;
     int mode = 0777;
+    int mask;
 
     if (!PyArg_ParseTuple(args, "iO&|i:mkdirat",
             &dirfd, PyUnicode_FSConverter, &opath, &mode))
@@ -8321,6 +8328,13 @@
     path = PyBytes_AsString(opath);
     Py_BEGIN_ALLOW_THREADS
     res = mkdirat(dirfd, path, mode);
+#ifdef HAVE_FCHMODAT
+    if (res == 0) {
+        mask = umask(0);
+        umask(mask);
+        res = fchmodat(dirfd, path, mode ^ mask, 0);
+    }
+#endif
     Py_END_ALLOW_THREADS
     Py_DECREF(opath);
     if (res < 0)