diff --git a/src/dodb/directed_graph.cr b/src/dodb/directed_graph.cr
index 6c39c74..e80f990 100644
--- a/src/dodb/directed_graph.cr
+++ b/src/dodb/directed_graph.cr
@@ -3,6 +3,8 @@ require "json"
 
 require "./indexer.cr"
 
+# WARNING: this code hasn't been reviewed nor used in years.
+
 class DODB::DirectedGraph(V) < DODB::Indexer(V)
 	property name         : String
 	property key_proc     : Proc(V, Array(String))