diff --git a/src/mark_sweep.cc b/src/mark_sweep.cc
index b3d21a3..307a804 100644
--- a/src/mark_sweep.cc
+++ b/src/mark_sweep.cc
@@ -31,6 +31,8 @@
 
   // TODO: if concurrent, clear the card table.
 
+  // TODO: if concurrent, enable card marking in compiler
+
   // TODO: check that the mark bitmap is entirely clear.
 
   return true;