diff --git a/libc/kernel/arch-x86/asm/pgtable-2level-defs.h b/libc/kernel/arch-x86/asm/pgtable-2level-defs.h
index 9edc6c5..9a60db5 100644
--- a/libc/kernel/arch-x86/asm/pgtable-2level-defs.h
+++ b/libc/kernel/arch-x86/asm/pgtable-2level-defs.h
@@ -7,16 +7,20 @@
  ***   structures, and macros generated from the original header, and thus,
  ***   contains no copyrightable information.
  ***
+ ***   To edit the content of this header, modify the corresponding
+ ***   source file (e.g. under external/kernel-headers/original/) then
+ ***   run bionic/libc/kernel/tools/update_all.py
+ ***
+ ***   Any manual change here will be lost the next time this script will
+ ***   be run. You've been warned!
+ ***
  ****************************************************************************
  ****************************************************************************/
 #ifndef _I386_PGTABLE_2LEVEL_DEFS_H
 #define _I386_PGTABLE_2LEVEL_DEFS_H
-
 #define SHARED_KERNEL_PMD 0
-
 #define PGDIR_SHIFT 22
+/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
 #define PTRS_PER_PGD 1024
-
 #define PTRS_PER_PTE 1024
-
 #endif