diff --git a/libc/kernel/arch-x86/asm/prctl.h b/libc/kernel/arch-x86/asm/prctl.h
index 8852ca7..d194cf8 100644
--- a/libc/kernel/arch-x86/asm/prctl.h
+++ b/libc/kernel/arch-x86/asm/prctl.h
@@ -7,14 +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 X86_64_PRCTL_H
 #define X86_64_PRCTL_H 1
-
 #define ARCH_SET_GS 0x1001
 #define ARCH_SET_FS 0x1002
+/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
 #define ARCH_GET_FS 0x1003
 #define ARCH_GET_GS 0x1004
-
 #endif