diff --git a/Lib/test/test_tokenize.py b/Lib/test/test_tokenize.py
--- a/Lib/test/test_tokenize.py
+++ b/Lib/test/test_tokenize.py
@@ -638,7 +638,7 @@
 from test import support
 from tokenize import (tokenize, _tokenize, untokenize, NUMBER, NAME, OP,
                      STRING, ENDMARKER, ENCODING, tok_name, detect_encoding,
-                     open as tokenize_open)
+                     TokenInfo, COMMENT, NL, open as tokenize_open)
 from io import BytesIO
 from unittest import TestCase
 import os, sys, glob
@@ -1109,6 +1109,75 @@
                                   token.NAME, token.AMPER, token.NUMBER,
                                   token.RPAR)
 
+    def test_untokenize_half_compat(self):
+        tokens = [
+                TokenInfo(ENCODING, 'utf-8', (0, 0), (0, 0), ''),
+                TokenInfo(COMMENT, '# some test source',
+                          (0, 0), (0, 18), '# some test source\n'),
+                (NL, '\n'),
+                (COMMENT, '# more test source'),
+                (ENDMARKER, ''),
+                ]
+        expected = b"# some test source\n# more test source"
+        source = untokenize(tokens)
+
+        self.assertEqual(source, expected)
+
+    def test_untokenize_half_compat_with_iterator(self):
+        tokens = [
+                TokenInfo(ENCODING, 'utf-8', (0, 0), (0, 0), ''),
+                TokenInfo(COMMENT, '# some test source',
+                          (0, 0), (0, 18), '# some test source\n'),
+                (NL, '\n'),
+                (COMMENT, '# more test source'),
+                (ENDMARKER, ''),
+                ]
+        expected = b"# some test source\n# more test source"
+        iter_tokens = iter(tokens)
+        source = untokenize(iter_tokens)
+
+        self.assertEqual(source, expected)
+
+    def test_untokenize_encoding_with_iterator(self):
+        tokens = [
+                TokenInfo(ENCODING, 'utf-8', (0, 0), (0, 0), ''),
+                TokenInfo(ENDMARKER, '', (0, 0), (0, 0), ''),
+                ]
+        iter_tokens = iter(tokens)
+
+        expected = untokenize(tokens)
+        source = untokenize(iter_tokens)
+
+        self.assertEqual(source, expected)
+
+    def test_untokenize_encoding_compat_mode(self):
+        tokens = [
+                TokenInfo(ENCODING, 'utf-8', (0, 0), (0, 0), ''),
+                TokenInfo(ENDMARKER, '', (0, 0), (0, 0), ''),
+                ]
+        truncated = [tok[:2] for tok in tokens]
+
+        expected = untokenize(tokens)
+        source = untokenize(truncated)
+
+        self.assertEqual(source, expected)
+
+
+    def test_untokenize_encoding_compat_mode_with_iterator(self):
+        tokens = [
+                TokenInfo(ENCODING, 'utf-8', (0, 0), (0, 0), ''),
+                TokenInfo(ENDMARKER, '', (0, 0), (0, 0), ''),
+                ]
+        truncated = (tok[:2] for tok in tokens)
+        iter_tokens = iter(tokens)
+
+        expected = untokenize(iter_tokens)
+        source = untokenize(truncated)
+
+        self.assertEqual(source, expected)
+
+
+
 __test__ = {"doctests" : doctests, 'decistmt': decistmt}
 
 def test_main():
diff --git a/Lib/tokenize.py b/Lib/tokenize.py
--- a/Lib/tokenize.py
+++ b/Lib/tokenize.py
@@ -30,6 +30,7 @@
 from token import *
 from codecs import lookup, BOM_UTF8
 import collections
+import itertools
 from io import TextIOWrapper
 cookie_re = re.compile("coding[:=]\s*([-\w.]+)")
 
@@ -234,6 +235,7 @@
             self.tokens.append(" " * col_offset)
 
     def untokenize(self, iterable):
+        iterable = iter(iterable)
         for t in iterable:
             if len(t) == 2:
                 self.compat(t, iterable)
@@ -261,7 +263,7 @@
         if toknum in (NEWLINE, NL):
             startline = True
         prevstring = False
-        for tok in iterable:
+        for tok in itertools.chain([token], iterable):
             toknum, tokval = tok[:2]
             if toknum == ENCODING:
                 self.encoding = tokval