diff --git a/.github/scripts/main/main.sh b/.github/scripts/main/main.sh
index 6f5385670f5..9dcf821463e 100644
--- a/.github/scripts/main/main.sh
+++ b/.github/scripts/main/main.sh
@@ -127,6 +127,9 @@ if [ "$OPAM_TEST" = "1" ]; then
   fi
   cd $CACHE/opam-rt
   git fetch origin
+  if [ "$GITHUB_EVENT_NAME" = "pull_request" ] && git ls-remote --exit-code origin $GITHUB_PR_USER/$BRANCH ; then
+    BRANCH=$GITHUB_PR_USER/$BRANCH
+  fi
   if git ls-remote --exit-code origin $BRANCH ; then
     if git branch | grep -q $BRANCH; then
       git checkout $BRANCH
diff --git a/.github/workflows/ci.ml b/.github/workflows/ci.ml
index 9ff06d19121..d2c33c5414d 100644
--- a/.github/workflows/ci.ml
+++ b/.github/workflows/ci.ml
@@ -378,7 +378,9 @@ let main_test_job ~analyse_job ~build_linux_job ~build_windows_job:_ ~build_macO
   let matrix = platform_ocaml_matrix ~fail_fast:false start_latests_ocaml in
   let host = host_of_platform platform in
   let ocamlv = "${{ matrix.ocamlv }}" in
-  job ~oc ~workflow ?section ~runs_on:(Runner [runner]) ~env:[("OPAM_TEST", "1")] ~matrix ~needs ("Test-" ^ name_of_platform platform)
+  job ~oc ~workflow ?section ~runs_on:(Runner [runner])
+    ~env:[("OPAM_TEST", "1"); ("GITHUB_PR_USER", "${{ github.event.pull_request.user.login }}")]
+    ~matrix ~needs ("Test-" ^ name_of_platform platform)
     ++ only_on MacOS (install_sys_packages ["coreutils"; "gpatch"] ~descr:"Install gnu coreutils" [MacOS])
     ++ checkout ()
     ++ only_on Linux (run "Install bubblewrap" ["sudo apt install bubblewrap"])
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 5ee3dc78f71..4bfa4c4c034 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -282,6 +282,7 @@ jobs:
       fail-fast: false
     env:
       OPAM_TEST: 1
+      GITHUB_PR_USER: ${{ github.event.pull_request.user.login }}
     steps:
     - name: Checkout tree
       uses: actions/checkout@v4
@@ -336,6 +337,7 @@ jobs:
       fail-fast: false
     env:
       OPAM_TEST: 1
+      GITHUB_PR_USER: ${{ github.event.pull_request.user.login }}
     steps:
     - name: Install gnu coreutils
       run: brew install coreutils gpatch