diff --git a/README.md b/README.md
index 3381774cb5e0a0e7f367eac237fd851f0f3156b5..7400a1e30f1c107dc6ea60bbe2d9f83410cc632b 100644
--- a/README.md
+++ b/README.md
@@ -69,6 +69,8 @@ active-repositories: hackage.haskell.org, head.hackage.ghc.haskell.org
 Also see
 https://cabal.readthedocs.io/en/latest/cabal-project.html#cfg-field-active-repositories.
 
+`HEAD.hackage` doesn't bump the bounds of boot packages + certain other packages to avoid the busywork of bumping them. When using `HEAD.hackage`, you should use `--allow-newer` for these packages. The full list is [here](https://gitlab.haskell.org/ghc/head.hackage/-/blob/90570e1c4606c1d7d3d41797ec1b32d1b984067b/ci/MakeConstraints.hs#L40-49).
+
 ### As an add-on remote repository
 
 It is *not* recommended to add the `HEAD.hackage` repository index to