#18430: Document that peek() may change the position of the underlying file for
the BZ2File, GzipFile and LZMAFile classes.
diff --git a/Doc/library/bz2.rst b/Doc/library/bz2.rst
index 95a5abb..b79bccd 100644
--- a/Doc/library/bz2.rst
+++ b/Doc/library/bz2.rst
@@ -91,6 +91,11 @@
byte of data will be returned (unless at EOF). The exact number of bytes
returned is unspecified.
+ .. note:: While calling :meth:`peek` does not change the file position of
+ the :class:`BZ2File`, it may change the position of the underlying file
+ object (e.g. if the :class:`BZ2File` was constructed by passing a file
+ object for *filename*).
+
.. versionadded:: 3.3
.. versionchanged:: 3.1