diff -r 4de15c54e59f -r c6061cadb400 hgext/blackbox.py
--- a/hgext/blackbox.py	Thu Feb 08 23:27:24 2018 +0530
+++ b/hgext/blackbox.py	Thu Feb 15 17:18:26 2018 +0100
@@ -49,6 +49,7 @@
     ui as uimod,
     util,
 )
+from mercurial.utils import dateutil
 
 # Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
 # extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
@@ -164,7 +165,7 @@
                 return
             ui._bbinlog = True
             default = self.configdate('devel', 'default-date')
-            date = util.datestr(default, '%Y/%m/%d %H:%M:%S')
+            date = dateutil.datestr(default, '%Y/%m/%d %H:%M:%S')
             user = util.getuser()
             pid = '%d' % util.getpid()
             formattedmsg = msg[0] % msg[1:]