diff --git a/doc/todo/type_level_port_conflict_detection.mdwn b/doc/todo/type_level_port_conflict_detection.mdwn
index 43118cd..5aec577 100644
--- a/doc/todo/type_level_port_conflict_detection.mdwn
+++ b/doc/todo/type_level_port_conflict_detection.mdwn
@@ -1 +1,5 @@
 See <http://stackoverflow.com/questions/26027765/using-types-to-prevent-conflicting-port-numbers-in-a-list> --[[Joey]]
+
+Needs ghc newer than 7.6.3. It may be possible to port Data.Type.Equality
+and Data.Type.Bool to older versions; I got them to compile but they didn't
+work right. --[[Joey]]