diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index bee648e..62e0d8b 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -122,6 +122,27 @@
 extern int    mknod(const char *, mode_t, dev_t);
 extern mode_t umask(mode_t);
 
+#if defined(__BIONIC_FORTIFY_INLINE)
+
+extern mode_t __umask_chk(mode_t);
+extern mode_t __umask_real(mode_t)
+    __asm__(__USER_LABEL_PREFIX__ "umask");
+extern void __umask_error()
+    __attribute__((__error__("umask called with invalid mode")));
+
+__BIONIC_FORTIFY_INLINE
+mode_t umask(mode_t mode) {
+  if (__builtin_constant_p(mode)) {
+    if ((mode & 0777) != mode) {
+      __umask_error();
+    }
+    return __umask_real(mode);
+  }
+  return __umask_chk(mode);
+}
+#endif /* defined(__BIONIC_FORTIFY_INLINE) */
+
+
 #define  stat64    stat
 #define  fstat64   fstat
 #define  lstat64   lstat