diff --git a/todo.txt b/todo.txt
index 75bfc73c..ce74206b 100644
--- a/todo.txt
+++ b/todo.txt
@@ -64,6 +64,9 @@
 
 * Rationalize support/unused.hpp and the ignore stuff needed for tie etc.
 
+* Why do we need to set FUSION_MAX_VECTOR_SIZE when we set
+  FUSION_MAX_MAP_SIZE?
+
 ==========================================================
 
 From the fusion review (please mark all done items):