diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -1858,6 +1858,19 @@
     tz = delta.days * 86400 + delta.seconds
     return timestamp, tz
 
+def hgdatetopython(date):
+    """Returns a Python datetime from a Mercurial tuple-style date"""
+    t, tz = date
+    d = t - tz
+    if d > 0x7fffffff:
+        d = 0x7fffffff
+    elif d < -0x80000000:
+        d = -0x80000000
+    # Never use time.gmtime() and datetime.datetime.fromtimestamp()
+    # because they use the gmtime() system call which is buggy on Windows
+    # for negative values.
+    return datetime.datetime(1970, 1, 1) + datetime.timedelta(seconds=d)
+
 def datestr(date=None, format='%a %b %d %H:%M:%S %Y %1%2'):
     """represent a (unixtime, offset) tuple as a localized time.
     unixtime is seconds since the epoch, and offset is the time zone's
@@ -1882,17 +1895,8 @@
         format = format.replace("%z", "%1%2")
         format = format.replace("%1", "%c%02d" % (sign, q))
         format = format.replace("%2", "%02d" % r)
-    d = t - tz
-    if d > 0x7fffffff:
-        d = 0x7fffffff
-    elif d < -0x80000000:
-        d = -0x80000000
-    # Never use time.gmtime() and datetime.datetime.fromtimestamp()
-    # because they use the gmtime() system call which is buggy on Windows
-    # for negative values.
-    t = datetime.datetime(1970, 1, 1) + datetime.timedelta(seconds=d)
-    s = encoding.strtolocal(t.strftime(encoding.strfromlocal(format)))
-    return s
+    t = hgdatetopython((t, tz))
+    return encoding.strtolocal(t.strftime(encoding.strfromlocal(format)))
 
 def shortdate(date=None):
     """turn (timestamp, tzoff) tuple into iso 8631 date."""