diff --git a/Help/command/ctest_start.rst b/Help/command/ctest_start.rst
index f16142e7b0..b5c7a179e9 100644
--- a/Help/command/ctest_start.rst
+++ b/Help/command/ctest_start.rst
@@ -14,3 +14,9 @@ CTEST_SOURCE_DIRECTORY and CTEST_BINARY_DIRECTORY.  If the track is
 specified, the submissions will go to the specified track.  If APPEND
 is used, the existing TAG is used rather than creating a new one based
 on the current time stamp.
+
+If the ``CTEST_CHECKOUT_COMMAND`` variable (or the ``CTEST_CVS_CHECKOUT``
+variable) is set, its content is treated as command-line.  The command is
+invoked with the current working directory set to the parent of the source
+directory, even if the source directory already exists.  This can be used
+to create the source tree from a version control repository.