diff -r f33fc2117bb2 Doc/reference/lexical_analysis.rst
--- a/Doc/reference/lexical_analysis.rst	Fri Sep 02 16:32:32 2016 -0700
+++ b/Doc/reference/lexical_analysis.rst	Sat Sep 03 22:40:04 2016 +0800
@@ -443,8 +443,8 @@
 
 Bytes literals are always prefixed with ``'b'`` or ``'B'``; they produce an
 instance of the :class:`bytes` type instead of the :class:`str` type.  They
-may only contain ASCII characters; bytes with a numeric value of 128 or greater
-must be expressed with escapes.
+may only contain ASCII characters; bytes with a numeric value of 127 or greater,
+or less than 32,  must be expressed with escapes.
 
 As of Python 3.3 it is possible again to prefix string literals with a
 ``u`` prefix to simplify maintenance of dual 2.x and 3.x codebases.