Index: Lib/imaplib.py
===================================================================
--- Lib/imaplib.py	(revision 88215)
+++ Lib/imaplib.py	(working copy)
@@ -1308,9 +1308,11 @@
 
 
 
-Mon2num = {'Jan': 1, 'Feb': 2, 'Mar': 3, 'Apr': 4, 'May': 5, 'Jun': 6,
-        'Jul': 7, 'Aug': 8, 'Sep': 9, 'Oct': 10, 'Nov': 11, 'Dec': 12}
+_month_names = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
+                'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
 
+Mon2num = dict(zip((x.encode() for x in _month_names), range(1, 13)))
+
 def Internaldate2tuple(resp):
     """Parse an IMAP4 INTERNALDATE string.
 
@@ -1401,17 +1403,21 @@
     else:
         raise ValueError("date_time not of a known type")
 
-    dt = time.strftime("%d-%b-%Y %H:%M:%S", tt)
-    if dt[0] == '0':
-        dt = ' ' + dt[1:]
     if time.daylight and tt[-1]:
         zone = -time.altzone
     else:
         zone = -time.timezone
-    return '"' + dt + " %+03d%02d" % divmod(zone//60, 60) + '"'
 
+    result = (('%02d-%s-%04d %02d:%02d:%02d' %
+               (tt[2], _month_names[tt[1] - 1], tt[0], tt[3], tt[4], tt[5])) +
+              (' %+03d%02d' % divmod(zone//60, 60)))
 
+    if result[0] == '0':
+        result = ' ' + result[1:]
 
+    return '"' + result + '"'
+
+
 if __name__ == '__main__':
 
     # To test: invoke either as 'python imaplib.py [IMAP4_server_hostname]'