diff --git a/gc.c b/gc.c
index fc4c458f..73f1fab6 100644
--- a/gc.c
+++ b/gc.c
@@ -826,6 +826,14 @@ void gc_mark_gray(gc_thread_data *thd, object obj)
   }
 }
 
+/**
+ * Add a pending write to the mark buffer.
+ * These are pended because they are written in a batch during minor GC.
+ * To prevent race conditions we wait until all of the writes are made before
+ * updating last write.
+ *
+ * TODO: figure out a new name for this function.
+ */
 void gc_mark_gray2(gc_thread_data *thd, object obj)
 {
   if (is_object_type(obj) && mark(obj) == gc_color_clear) {