diff --git a/Lib/difflib.py b/Lib/difflib.py
index 292bba9..92d58fa 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1160,18 +1160,18 @@
 
     The unidiff format normally has a header for filenames and modification
     times.  Any or all of these may be specified using strings for
-    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.  The modification
-    times are normally expressed in the format returned by time.ctime().
+    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
+    The modification times are normally expressed in the ISO 8601 format.
 
     Example:
 
     >>> for line in unified_diff('one two three four'.split(),
     ...             'zero one tree four'.split(), 'Original', 'Current',
-    ...             'Sat Jan 26 23:30:50 1991', 'Fri Jun 06 10:20:52 2003',
+    ...             '2005-01-26 23:30:50', '2010-04-02 10:20:52',
     ...             lineterm=''):
-    ...     print(line)
-    --- Original Sat Jan 26 23:30:50 1991
-    +++ Current Fri Jun 06 10:20:52 2003
+    ...     print(line)                 # doctest: +NORMALIZE_WHITESPACE
+    --- Original        2005-01-26 23:30:50
+    +++ Current         2010-04-02 10:20:52
     @@ -1,4 +1,4 @@
     +zero
      one
@@ -1184,8 +1184,10 @@
     started = False
     for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
         if not started:
-            yield '--- %s %s%s' % (fromfile, fromfiledate, lineterm)
-            yield '+++ %s %s%s' % (tofile, tofiledate, lineterm)
+            fromdate = '\t%s' % fromfiledate if fromfiledate else ''
+            todate = '\t%s' % tofiledate if tofiledate else ''
+            yield '--- %s%s%s' % (fromfile, fromdate, lineterm)
+            yield '+++ %s%s%s' % (tofile, todate, lineterm)
             started = True
         i1, i2, j1, j2 = group[0][1], group[-1][2], group[0][3], group[-1][4]
         yield "@@ -%d,%d +%d,%d @@%s" % (i1+1, i2-i1, j1+1, j2-j1, lineterm)
@@ -1223,17 +1225,16 @@
     The context diff format normally has a header for filenames and
     modification times.  Any or all of these may be specified using
     strings for 'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
-    The modification times are normally expressed in the format returned
-    by time.ctime().  If not specified, the strings default to blanks.
+    The modification times are normally expressed in the ISO 8601 format.
+    If not specified, the strings default to blanks.
 
     Example:
 
     >>> print(''.join(context_diff('one\ntwo\nthree\nfour\n'.splitlines(1),
-    ...       'zero\none\ntree\nfour\n'.splitlines(1), 'Original', 'Current',
-    ...       'Sat Jan 26 23:30:50 1991', 'Fri Jun 06 10:22:46 2003')),
+    ...       'zero\none\ntree\nfour\n'.splitlines(1), 'Original', 'Current')),
     ...       end="")
-    *** Original Sat Jan 26 23:30:50 1991
-    --- Current Fri Jun 06 10:22:46 2003
+    *** Original
+    --- Current
     ***************
     *** 1,4 ****
       one
@@ -1251,8 +1252,10 @@
     prefixmap = {'insert':'+ ', 'delete':'- ', 'replace':'! ', 'equal':'  '}
     for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
         if not started:
-            yield '*** %s %s%s' % (fromfile, fromfiledate, lineterm)
-            yield '--- %s %s%s' % (tofile, tofiledate, lineterm)
+            fromdate = '\t%s' % fromfiledate if fromfiledate else ''
+            todate = '\t%s' % tofiledate if tofiledate else ''
+            yield '*** %s%s%s' % (fromfile, fromdate, lineterm)
+            yield '--- %s%s%s' % (tofile, todate, lineterm)
             started = True
 
         yield '***************%s' % (lineterm,)
diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index 852aae9..6c9bde6 100644
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -159,10 +159,32 @@
         difflib.SequenceMatcher(None, old, new).get_opcodes()
 
 
+class TestOutputFormat(unittest.TestCase):
+    def test_tab_delimiter(self):
+        args = ['one', 'two', 'Original', 'Current',
+            '2005-01-26 23:30:50', '2010-04-02 10:20:52']
+        ud = difflib.unified_diff(*args, lineterm='')
+        self.assertEqual(list(ud)[0:2], [
+                           "--- Original\t2005-01-26 23:30:50",
+                           "+++ Current\t2010-04-02 10:20:52"])
+        cd = difflib.context_diff(*args, lineterm='')
+        self.assertEqual(list(cd)[0:2], [
+                           "*** Original\t2005-01-26 23:30:50",
+                           "--- Current\t2010-04-02 10:20:52"])
+
+    def test_no_trailing_tab_on_empty_filedate(self):
+        args = ['one', 'two', 'Original', 'Current']
+        ud = difflib.unified_diff(*args, lineterm='')
+        self.assertEqual(list(ud)[0:2], ["--- Original", "+++ Current"])
+
+        cd = difflib.context_diff(*args, lineterm='')
+        self.assertEqual(list(cd)[0:2], ["*** Original", "--- Current"])
+
+
 def test_main():
     difflib.HtmlDiff._default_prefix = 0
     Doctests = doctest.DocTestSuite(difflib)
-    run_unittest(TestSFpatches, TestSFbugs, Doctests)
+    run_unittest(TestSFpatches, TestSFbugs, TestOutputFormat, Doctests)
 
 if __name__ == '__main__':
     test_main()