diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index a767570..5fcfba7 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -124,6 +124,8 @@
                 arguments. This setting is useful for tests.
         board: Boards() object to use, containing a list of available
                 boards. If this is None it will be created and scanned.
+        clean_dir: Used for tests only, indicates that the existing output_dir
+            should be removed before starting the build
     """
     global builder