diff --git a/sphinx/source/setup.rst b/sphinx/source/setup.rst
index 838a019..d8b1b4e 100644
--- a/sphinx/source/setup.rst
+++ b/sphinx/source/setup.rst
@@ -831,6 +831,8 @@ it hasn't already been done so by an earlier invocation.
 library specified by one the Config files traversed by the setup
 tool. 
 
+*-mconly* forces the setup tool to only run the macro processor. Processed files
+are saved to the object directory.
 
 
 .. _`Sec:SetupShortcuts`: