--- a/Lib/tarfile.py    Wed Aug 06 22:50:30 2014 -0700
+++ b/Lib/tarfile.py    Thu Aug 07 12:57:12 2014 +0200
@@ -412,7 +412,7 @@
         """Initialize for writing with gzip compression.
         """
         self.cmp = self.zlib.compressobj(9, self.zlib.DEFLATED,
-                                            -self.zlib.MAX_WBITS,
+                                            self.zlib.MAX_WBITS,
                                             self.zlib.DEF_MEM_LEVEL,
                                             0)
         timestamp = struct.pack("<L", int(time.time()))
@@ -472,7 +472,7 @@
     def _init_read_gz(self):
         """Initialize for reading a gzip compressed fileobj.
         """
-        self.cmp = self.zlib.decompressobj(-self.zlib.MAX_WBITS)
+        self.cmp = self.zlib.decompressobj(self.zlib.MAX_WBITS)
         self.dbuf = b""
 
         # taken from gzip.GzipFile with some alterations