--- a/hgext/blackbox.py	Tue Jul 11 12:27:58 2017 +0200
+++ b/hgext/blackbox.py	Tue Jul 11 12:38:17 2017 +0200
@@ -234,6 +234,7 @@
 
     if util.safehasattr(ui, 'setrepo'):
         ui.setrepo(repo)
+    repo._wlockfreeprefix.add('blackbox.log')
 
 @command('^blackbox',
     [('l', 'limit', 10, _('the number of events to show')),