mention -n
diff --git a/Doc/library/2to3.rst b/Doc/library/2to3.rst
index 27626e0..9852821 100644
--- a/Doc/library/2to3.rst
+++ b/Doc/library/2to3.rst
@@ -37,8 +37,8 @@
A diff against the original source file is printed. 2to3 can also write the
needed modifications right back to the source file. (Of course, a backup of the
-original is also be made.) Writing the changes back is enabled with the
-:option:`-w` flag::
+original is also be made unless :option:`-n` is also given.) Writing the
+changes back is enabled with the :option:`-w` flag::
$ 2to3 -w example.py