wbits negative was documented SEVEN years ago
diff --git a/Doc/library/zlib.rst b/Doc/library/zlib.rst
index 7d9859b..0118704 100644
--- a/Doc/library/zlib.rst
+++ b/Doc/library/zlib.rst
@@ -127,9 +127,7 @@
than the size originally used to compress the stream; using a too-small
value will result in an exception. The default value is therefore the
highest value, 15. When *wbits* is negative, the standard
- :program:`gzip` header is suppressed; this is an undocumented feature of the
- zlib library, used for compatibility with :program:`unzip`'s compression file
- format.
+ :program:`gzip` header is suppressed.
*bufsize* is the initial size of the buffer used to hold decompressed data. If
more space is required, the buffer size will be increased as needed, so you