diff --git a/overlays/haskell.nix b/overlays/haskell.nix
index 9f21f2704d..49c1c594c8 100644
--- a/overlays/haskell.nix
+++ b/overlays/haskell.nix
@@ -306,7 +306,7 @@ final: prev: {
         # If you want to update this value it important to check the
         # materializations.  Turn `checkMaterialization` on below and
         # check the CI results before turning it off again.
-        internalHackageIndexState = "2022-11-06T00:00:00Z";
+        internalHackageIndexState = "2022-11-06T00:00:00Z"; # Remember to also update ../nix-tools/cabal.project and ../nix-tools/flake.lock
 
         checkMaterialization = false; # This is the default. Use an overlay to set it to true and test all the materialized files