checkpw: -ERR unable to write pipe

When I try testing checkpassword according to djb's instructions
(http://cr.yp.to/checkpwd/install.html) I get the following error:

  -ERR unable to write pipe

I'm using Gerrit's packages exclusively:

  $ dpkg -l | grep checkp\|qmail
  ii  checkpw                  1.00-3
  ii  dot-forward              0.71-zarge1
  ii  fastforward              0.51-zarge1
  ii  qmail                    1.03-zarge1
  ii  qmail-run                1.1.0
  ii  qmail-uids-gids          1.1.0

I've searched gmane.comp.djb.checkpassword to no avail.  (There are
three posts by people experiencing precisely this problem, each of
them unanswered!)

Of course, I've no doubt a 'Debian centred' list won't replicate this
behaviour, such is our powerful sense of community ;-)

sdt