diff --git a/doc/man/sphinx-build.rst b/doc/man/sphinx-build.rst
index 46f213989..fdd0d36c2 100644
--- a/doc/man/sphinx-build.rst
+++ b/doc/man/sphinx-build.rst
@@ -143,11 +143,15 @@ Options
 
    Distribute the build over *N* processes in parallel, to make building on
    multiprocessor machines more effective.  Note that not all parts and not all
-   builders of Sphinx can be parallelized.
+   builders of Sphinx can be parallelized.  If ``auto`` argument is given,
+   Sphinx uses the number of CPUs as *N*.
 
    .. versionadded:: 1.2
       This option should be considered *experimental*.
 
+   .. versionchanged:: 1.7
+      Support ``auto`` argument.
+
 .. option:: -c path
 
    Don't look for the :file:`conf.py` in the source directory, but use the given