diff --git a/ci/workflows/main-cron.yml b/ci/workflows/main-cron.yml
index 1c2083e1a0d4..d35803e02d75 100644
--- a/ci/workflows/main-cron.yml
+++ b/ci/workflows/main-cron.yml
@@ -712,6 +712,8 @@ steps:
           run: source-test-env
           config: ci/docker-compose.yml
           mount-buildkite-agent: true
+          environment:
+            - BUILDKITE_BRANCH
       - ./ci/plugins/upload-failure-logs
     matrix:
       setup:
diff --git a/ci/workflows/pull-request.yml b/ci/workflows/pull-request.yml
index c76589e95afd..151d5ce6ec05 100644
--- a/ci/workflows/pull-request.yml
+++ b/ci/workflows/pull-request.yml
@@ -711,6 +711,8 @@ steps:
           run: source-test-env
           config: ci/docker-compose.yml
           mount-buildkite-agent: true
+          environment:
+            - BUILDKITE_BRANCH
       - ./ci/plugins/upload-failure-logs
     matrix:
       setup:
diff --git a/e2e_test/backwards-compat-tests/scripts/utils.sh b/e2e_test/backwards-compat-tests/scripts/utils.sh
index f66e7518df2e..3f99565b9870 100644
--- a/e2e_test/backwards-compat-tests/scripts/utils.sh
+++ b/e2e_test/backwards-compat-tests/scripts/utils.sh
@@ -138,7 +138,10 @@ get_old_version() {
 
   # We handle the edge case where the current branch is the one being released.
   # If so, we need to prune it from the list.
-  local current_branch=$(git branch --show-current | tr -d 'v')
+  # We cannot simply use 'git branch --show-current', because buildkite checks out with the commit,
+  # rather than branch. So the current state is detached.
+  # Instead we rely on BUILDKITE_BRANCH, provided by buildkite.
+  local current_branch=$(echo "$BUILDKITE_BRANCH" | tr -d 'v')
   echo "--- CURRENT BRANCH: $current_branch"
 
   echo "--- PRUNED VERSIONS"
@@ -147,7 +150,7 @@ get_old_version() {
 
   # Then we take the Nth latest version.
   # We set $OLD_VERSION to this.
-  OLD_VERSION=$(echo -e "$sorted_versions" | tail -n $VERSION_OFFSET | head -1)
+  OLD_VERSION=$(echo -e "$pruned_versions" | tail -n $VERSION_OFFSET | head -1)
 }
 
 get_new_version() {