diff --git a/.github/actions/setup-ocaml/action.yml b/.github/actions/setup-ocaml/action.yml
index fc8c788610..97098cf74f 100644
--- a/.github/actions/setup-ocaml/action.yml
+++ b/.github/actions/setup-ocaml/action.yml
@@ -104,6 +104,11 @@ runs:
       uses: ocaml/setup-ocaml@v3.8.0
       with:
         ocaml-compiler: ${{ inputs.compiler }}
+        # Use the HTTP repository to prevent intermittent CI setup failures:
+        # the Git-backed default can race with detached Git maintenance while
+        # OPAM scans it (https://github.com/ocaml/opam/issues/7031).
+        opam-repositories: |
+          default: https://opam.ocaml.org
         opam-pin: false
         cache: false
 
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c26588ac4b..baa311be88 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -117,7 +117,7 @@ jobs:
         with:
           compiler: ${{ matrix.ocaml_compiler }}
           os: ${{ matrix.os }}
-          cache-prefix: opam-env-v8
+          cache-prefix: opam-env-v9
 
       - name: Compiler build state key
         id: compiler-build-state-key
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index af2f13cbbe..733caa109e 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -44,7 +44,7 @@ jobs:
         with:
           compiler: ${{ env.OCAML_COMPILER }}
           os: ${{ env.OS }}
-          cache-prefix: opam-coverage-v1
+          cache-prefix: opam-coverage-v2
           dependency-flags: --deps-only --with-test --with-dev-setup
 
       - name: Install OCaml coverage tooling