diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 74731ec679cf..26606fb4efd1 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -6,6 +6,9 @@ CHANGELOG
 Next Release (TBD)
 ==================
 
+* bugfix: ``aws s3 sync``: Fix issue for unnecessarily resyncing files
+  on windows machines.
+  (`issue 843 <https://github.com/aws/aws-cli/issues/843>`__)
 * bugfix: ``aws s3 sync``: Fix issue where keys were being decoded twice
   when syncing between buckets.
   (`issue 862 <https://github.com/aws/aws-cli/pull/862>`__)
diff --git a/awscli/customizations/s3/filegenerator.py b/awscli/customizations/s3/filegenerator.py
index f78169c80286..16284830cc76 100644
--- a/awscli/customizations/s3/filegenerator.py
+++ b/awscli/customizations/s3/filegenerator.py
@@ -124,7 +124,7 @@ def list_files(self, path, dir_op):
                     file_path = join(path, name)
                     if isdir(file_path):
                         names[i] = name + os.path.sep
-                names.sort()
+                self.normalize_sort(names, os.sep, '/')
                 for name in names:
                     file_path = join(path, name)
                     if not self.should_ignore_file(file_path):
@@ -141,6 +141,15 @@ def list_files(self, path, dir_op):
                             size, last_update = get_file_stat(file_path)
                             yield file_path, size, last_update
 
+    def normalize_sort(self, names, os_sep, character):
+        """
+        The purpose of this function is to ensure that the same path seperator
+        is used when sorting.  In windows, the path operator is a backslash as
+        opposed to a forward slash which can lead to differences in sorting
+        between s3 and a windows machine.
+        """
+        names.sort(key=lambda item: item.replace(os_sep, character))
+
     def _check_paths_decoded(self, path, names):
         # We can get a UnicodeDecodeError if we try to listdir(<unicode>) and
         # can't decode the contents with sys.getfilesystemencoding().  In this
diff --git a/tests/integration/customizations/s3/test_plugin.py b/tests/integration/customizations/s3/test_plugin.py
index 336de2d679c2..4301ea477320 100644
--- a/tests/integration/customizations/s3/test_plugin.py
+++ b/tests/integration/customizations/s3/test_plugin.py
@@ -478,6 +478,22 @@ def test_s3_to_s3_sync_with_plus_char(self):
         p2 = aws('s3 sync s3://%s/ s3://%s/' % (bucket_name, bucket_name_2))
         self.assertNotIn('copy:', p2.stdout)
         self.assertEqual('', p2.stdout)
+    
+    def test_sync_no_resync(self):
+        self.files.create_file('xyz123456789', contents='test1')
+        self.files.create_file(os.path.join('xyz1', 'test'), contents='test2')
+        self.files.create_file(os.path.join('xyz', 'test'), contents='test3')
+        bucket_name = self.create_bucket()
+        
+        p = aws('s3 sync %s s3://%s' % (self.files.rootdir, bucket_name))
+        self.assert_no_errors(p)
+        self.assertTrue(self.key_exists(bucket_name, 'xyz123456789'))
+        self.assertTrue(self.key_exists(bucket_name, 'xyz1/test'))
+        self.assertTrue(self.key_exists(bucket_name, 'xyz/test'))
+
+        p2 = aws('s3 sync %s s3://%s/' % (self.files.rootdir, bucket_name))
+        self.assertNotIn('upload:', p2.stdout)
+        self.assertEqual('', p2.stdout)
 
     def test_sync_to_from_s3(self):
         bucket_name = self.create_bucket()
diff --git a/tests/unit/customizations/s3/test_filegenerator.py b/tests/unit/customizations/s3/test_filegenerator.py
index 8efa04a893c9..79a13df57ba1 100644
--- a/tests/unit/customizations/s3/test_filegenerator.py
+++ b/tests/unit/customizations/s3/test_filegenerator.py
@@ -344,6 +344,28 @@ def test_list_local_files_with_unicode_chars(self):
         self.assertEqual(values, expected_order)
 
 
+class TestNormalizeSort(unittest.TestCase):
+    def test_normalize_sort(self):
+        names = ['xyz123456789',
+                 'xyz1' + os.path.sep + 'test',
+                 'xyz' + os.path.sep + 'test']
+        ref_names = [names[2], names[1], names[0]]
+        filegenerator = FileGenerator(None, None, None)
+        filegenerator.normalize_sort(names, os.path.sep, '/')
+        for i in range(len(ref_names)):
+            self.assertEqual(ref_names[i], names[i])
+    
+    def test_normalize_sort_backslash(self):
+        names = ['xyz123456789',
+                 'xyz1\\test',
+                 'xyz\\test']
+        ref_names = [names[2], names[1], names[0]]
+        filegenerator = FileGenerator(None, None, None)
+        filegenerator.normalize_sort(names, '\\', '/')
+        for i in range(len(ref_names)):
+            self.assertEqual(ref_names[i], names[i])
+
+
 class S3FileGeneratorTest(unittest.TestCase):
     def setUp(self):
         self.session = FakeSession()