diff --git a/rattail_tempmon/commands.py b/rattail_tempmon/commands.py
index e06ecca..7e6b8e8 100644
--- a/rattail_tempmon/commands.py
+++ b/rattail_tempmon/commands.py
@@ -183,7 +183,7 @@ class PurgeTempmon(Subcommand):
         do_purge(self.config, args.keep, dry_run=args.dry_run, progress=self.progress)
 
 
-def do_purge(self, config, keep_days, dry_run=False, progress=None):
+def do_purge(config, keep_days, dry_run=False, progress=None):
     from rattail_tempmon.db import Session, model
     from rattail.db.util import finalize_session