diff --git a/usr.sbin/pmcannotate/pmcannotate.c b/usr.sbin/pmcannotate/pmcannotate.c
index df547e37735..b22d0dc8278 100644
--- a/usr.sbin/pmcannotate/pmcannotate.c
+++ b/usr.sbin/pmcannotate/pmcannotate.c
@@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
 
 #include <unistd.h>
 
+/* NB: Make sure FNBUFF is as large as LNBUFF, otherwise it could overflow */
 #define	FNBUFF	512
 #define	LNBUFF	512