diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 736974576e2d685a2bd68d08b7658bbcee5fd7f8..a0b5f15c92cf0bcfc9c9a773f3b8390bdcd19999 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1297,6 +1297,8 @@ int format_decode(const char *fmt, struct printf_spec *spec)
  *   case.
  * %n is ignored
  *
+ * ** Please update Documentation/printk-formats.txt when making changes **
+ *
  * The return value is the number of characters which would
  * be generated for the given input, excluding the trailing
  * '\0', as per ISO C99. If you want to have the exact