implicit lock in formail

["Marco C ." <magicdice@inwind.it>]

Hi guys!!!
Every time I run fetchmail->procmail->formail, I get this message in procmail.log:

procmail: Couldn't determine implicit lockfile from "/usr/bin/formail"

The only place where I use formail is in .procmailrc, where I put the lines:
# cancels the header Received:
:0fhw:
| $FORMAIL -I Received:          # I defined FORMAIL = /usr/bin/formail 

This filter does its work, but the log file continues to warn me!!!
Can you help me? (as in three imaginary boys...)

Thanks in advance, marco

-- 
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
G!/MU d-(--) s:- a-- C++@ UL>++ P>+ L++>++++ E----@ 
W+>++ N- o? K- w-- O--@ M->+ V- PS+ PE-@ Y PGP- t-- 
5? X-- R-(*) tv+>++ b+ DI+@ D- G>++ e++ h-- r% y--@ 
------END GEEK CODE BLOCK------