diff --git a/.gitea/ci/bootstrap_workspace.sh b/.gitea/ci/bootstrap_workspace.sh
index f4b2040..8a0c153 100644
--- a/.gitea/ci/bootstrap_workspace.sh
+++ b/.gitea/ci/bootstrap_workspace.sh
@@ -128,7 +128,7 @@ create_job_workspace_from_mirror() {
 
     rm -rf "${job_workspace}"
     mkdir -p "${job_workspace}"
-    git clone --local "${mirror_path}" "${repo_dir}" >/dev/null
+    git clone --shared "${mirror_path}" "${repo_dir}" >/dev/null
     git -C "${repo_dir}" remote set-url origin "${remote_url}"
 }
 
diff --git a/tests/workspace_helper_test.sh b/tests/workspace_helper_test.sh
index 0518657..ce25081 100644
--- a/tests/workspace_helper_test.sh
+++ b/tests/workspace_helper_test.sh
@@ -71,7 +71,7 @@ test_repo_owner_and_name_parsing() {
 
 test_prepare_and_cleanup_workspace() {
     local temp_root remote_repo seed_repo mirror_root workspace_root env_file
-    local repo_dir mirror_path job_workspace origin_url
+    local repo_dir mirror_path job_workspace origin_url alternates_file alternates_target
 
     temp_root=$(mktemp -d)
     remote_repo="${temp_root}/remote.git"
@@ -117,6 +117,15 @@ test_prepare_and_cleanup_workspace() {
     origin_url=$(git -C "${repo_dir}" remote get-url origin)
     assert_eq "${remote_repo}" "${origin_url}" "prepared repo should point origin to the requested remote"
 
+    alternates_file="${repo_dir}/.git/objects/info/alternates"
+    if [ ! -f "${alternates_file}" ]; then
+        echo "FAIL: prepared repo should use shared mirror objects via alternates" >&2
+        exit 1
+    fi
+
+    alternates_target=$(cat "${alternates_file}")
+    assert_eq "${mirror_path}/objects" "${alternates_target}" "prepared repo should borrow objects from the bare mirror"
+
     cleanup_job_workspace "${job_workspace}"
 
     if [ -e "${job_workspace}" ]; then