diff -r 142891ab6e89 -r ab6468270b83 hgext/blackbox.py
--- a/hgext/blackbox.py	Wed Feb 03 18:15:18 2016 +0000
+++ b/hgext/blackbox.py	Wed Feb 03 15:18:29 2016 +0000
@@ -112,6 +112,7 @@
                 try:
                     blackbox.write('%s %s (%s)> %s' %
                                    (date, user, pid, formattedmsg))
+                    blackbox.flush()
                 except IOError as err:
                     self.debug('warning: cannot write to blackbox.log: %s\n' %
                                err.strerror)