diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 14ed041..56a1330 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -41,6 +41,6 @@ jobs:
       - run: opam exec -- dune build -p mlx,ocamlmerlin-mlx
 
         # TODO: pass --with-dev-setup to opam instead? (requires opam 2.2, I think)
-      - run: opam install menhir.20210419 menhirLib.20210419 menhirSdk.20210419 ocamlformat
+      - run: opam install menhir.20201216 menhirLib.20201216 menhirSdk.20201216 ocamlformat
 
       - run: opam exec -- dune runtest
diff --git a/mlx.opam b/mlx.opam
index 8f25b08..19577e9 100644
--- a/mlx.opam
+++ b/mlx.opam
@@ -9,6 +9,7 @@ doc: "https://url/to/documentation"
 bug-reports: "https://github.com/andreypopp/mlx/issues"
 depends: [
   "ocaml"
+  "ppxlib"
   "dune" {>= "3.9"}
   "menhir" {= "20210419" & with-dev-setup}
   "ocamlformat" {with-dev-setup}
diff --git a/ocamlmerlin-mlx.opam b/ocamlmerlin-mlx.opam
index 42acc2e..f438853 100644
--- a/ocamlmerlin-mlx.opam
+++ b/ocamlmerlin-mlx.opam
@@ -9,6 +9,7 @@ doc: "https://url/to/documentation"
 bug-reports: "https://github.com/andreypopp/mlx/issues"
 depends: [
   "ocaml"
+  "ppxlib"
   "dune" {>= "3.9"}
   "merlin-lib"
   "csexp" {with-dev-setup}