diff -r 6ba86ca875a8 Lib/gzip.py
--- a/Lib/gzip.py	Fri Jul 15 12:16:42 2016 -0700
+++ b/Lib/gzip.py	Sat Jul 16 11:56:18 2016 +0300
@@ -238,7 +238,17 @@
             mtime = time.time()
         write32u(self.fileobj, int(mtime))
         self.fileobj.write(b'\002')
-        self.fileobj.write(b'\377')
+
+        if os.name == 'nt':
+            if sys.getwindowsversion().platform == 2:  # NTFS
+                self.fileobj.write(b'\013')
+            else:
+                self.fileobj.write(b'\000')  # FAT
+        elif os.name == 'posix':
+                self.fileobj.write(b'\003')  # *NIX
+        else:
+            self.fileobj.write(b'\377')  # Unknown
+
         if fname:
             self.fileobj.write(fname + b'\000')
 
diff -r 6ba86ca875a8 Lib/test/test_gzip.py
--- a/Lib/test/test_gzip.py	Fri Jul 15 12:16:42 2016 -0700
+++ b/Lib/test/test_gzip.py	Sat Jul 16 11:56:18 2016 +0300
@@ -4,6 +4,7 @@
 import unittest
 from test import support
 from test.support import bigmemtest, _4G
+import sys
 import os
 import io
 import struct
@@ -317,7 +318,12 @@
             self.assertEqual(xflByte, b'\x02') # maximum compression
 
             osByte = fRead.read(1)
-            self.assertEqual(osByte, b'\xff') # OS "unknown" (OS-independent)
+            if os.name == 'nt':  # Windows
+                self.assertIn(osByte, [b'\013', b'\000'])
+            elif os.name == 'posix':
+                self.assertEqual(osByte, b'\003')  # *NIX
+            else:
+                self.assertEqual(osByte, b'\377')  # Unknown
 
             # Since the FNAME flag is set, the zero-terminated filename follows.
             # RFC 1952 specifies that this is the name of the input file, if any.