diff --git a/.github/workflows/gh-pages.yml b/.github/workflows/gh-pages.yml
index 99fd13c0..f1492d9f 100644
--- a/.github/workflows/gh-pages.yml
+++ b/.github/workflows/gh-pages.yml
@@ -16,7 +16,7 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ~/.opam
-          key: opam-${{ matrix.os }}-${{ matrix.ocaml }}
+          key: opam-ubuntu-latest-4.12.0
 
       - uses: avsm/setup-ocaml@v1
         with: