Getting error when trying to stop maldet

usually a "maldet -k" stops maldet. However:

Code:

root@mike:/# /usr/local/sbin/maldet -k
Linux Malware Detect v1.5
            (C) 2002-2016, R-fx Networks <[email protected]>
            (C) 2016, Ryan MacDonald <[email protected]>
This program may be freely redistributed under the terms of the GNU GPL v2

maldet(6380): {mon} sent kill to monitor service
error: list of process IDs must follow -p

Usage:
ps [options]

Try 'ps --help <simple|list|output|threads|misc|all>'
  or 'ps --help <s|l|o|t|m|a>'
for additional help text.

For more details see ps(1).

Any ideas?