#7191: describe more details of wbits parameter
diff --git a/Doc/library/zlib.rst b/Doc/library/zlib.rst
index 919b4e4..7d9859b 100644
--- a/Doc/library/zlib.rst
+++ b/Doc/library/zlib.rst
@@ -115,14 +115,18 @@
Decompresses the data in *string*, returning a string containing the
uncompressed data. The *wbits* parameter controls the size of the window
- buffer. If *bufsize* is given, it is used as the initial size of the output
+ buffer, and is discussed further below.
+ If *bufsize* is given, it is used as the initial size of the output
buffer. Raises the :exc:`error` exception if any error occurs.
The absolute value of *wbits* is the base two logarithm of the size of the
history buffer (the "window size") used when compressing data. Its absolute
value should be between 8 and 15 for the most recent versions of the zlib
library, larger values resulting in better compression at the expense of greater
- memory usage. The default value is 15. When *wbits* is negative, the standard
+ memory usage. When decompressing a stream, *wbits* must not be smaller
+ 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.