diff --git a/Doc/library/zlib.rst b/Doc/library/zlib.rst
index 1e2df00..9cffe27 100644
--- a/Doc/library/zlib.rst
+++ b/Doc/library/zlib.rst
@@ -160,6 +160,7 @@
      must include a zlib header and trailer.
 
    * 0: Automatically determine the window size from the zlib header.
+     Only supported since zlib 1.2.3.5.
 
    * −8 to −15: Uses the absolute value of *wbits* as the window size
      logarithm.  The input must be a raw stream with no header or trailer.
diff --git a/Lib/test/test_zlib.py b/Lib/test/test_zlib.py
index c537c2a..96cc3a7 100644
--- a/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@ -531,7 +531,6 @@
         co = zlib.compressobj(1, zlib.DEFLATED, 15)
         zlib15 = co.compress(HAMLET_SCENE) + co.flush()
         self.assertEqual(zlib.decompress(zlib15, 15), HAMLET_SCENE)
-        self.assertEqual(zlib.decompress(zlib15, 0), HAMLET_SCENE)
         self.assertEqual(zlib.decompress(zlib15, 32 + 15), HAMLET_SCENE)
         with self.assertRaisesRegexp(zlib.error, 'invalid window size'):
             zlib.decompress(zlib15, 14)
@@ -545,7 +544,6 @@
         zlib9 = co.compress(HAMLET_SCENE) + co.flush()
         self.assertEqual(zlib.decompress(zlib9, 9), HAMLET_SCENE)
         self.assertEqual(zlib.decompress(zlib9, 15), HAMLET_SCENE)
-        self.assertEqual(zlib.decompress(zlib9, 0), HAMLET_SCENE)
         self.assertEqual(zlib.decompress(zlib9, 32 + 9), HAMLET_SCENE)
         dco = zlib.decompressobj(32 + 9)
         self.assertEqual(dco.decompress(zlib9), HAMLET_SCENE)