diff --git a/doc/todo.txt b/doc/todo.txt
index 8d7ca3d..83861b2 100644
--- a/doc/todo.txt
+++ b/doc/todo.txt
@@ -64,5 +64,12 @@ for example or if perhaps you just don't have/want python for vim: >
   1 - Load (default)
   0 - Don't load
 
+                                                      *'g:todo_done_filename'*
+Specify a custom filename for completed todo entries to be archived to. Useful
+for compatibility with other todo.txt editors, or as a matter of preference:
+  let g:todo_done_filename = 'completed.txt'
+
+   Default: Done.txt or done.txt based on todo.txt capitalization.
+
 ===============================================================================
 vim:ft=help:et:ts=2:sw=2:sts=2:norl