diff -r 4de15c54e59f -r c6061cadb400 mercurial/patch.py
--- a/mercurial/patch.py	Thu Feb 08 23:27:24 2018 +0530
+++ b/mercurial/patch.py	Thu Feb 15 17:18:26 2018 +0100
@@ -40,6 +40,7 @@
     util,
     vfs as vfsmod,
 )
+from .utils import dateutil
 
 diffhelpers = policy.importmod(r'diffhelpers')
 stringio = util.stringio
@@ -2669,8 +2670,8 @@
     def isempty(fctx):
         return fctx is None or fctx.size() == 0
 
-    date1 = util.datestr(ctx1.date())
-    date2 = util.datestr(ctx2.date())
+    date1 = dateutil.datestr(ctx1.date())
+    date2 = dateutil.datestr(ctx2.date())
 
     gitmode = {'l': '120000', 'x': '100755', '': '100644'}