diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 1286c232..e707c1de 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -61,7 +61,8 @@ jobs:
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with:
-          ocaml-compiler: 5
+          ocaml-compiler: 4
+          opam-pin: false
 
       - run: opam install "mirage<4.7.0"
       - run: opam exec -- mirage configure -t ${{ matrix.mode }}