diff --git a/actions/example-pull-request/.forgejo/workflows/test.yml b/actions/example-pull-request/.forgejo/workflows/test.yml
index 91a906d..90e9fb4 100644
--- a/actions/example-pull-request/.forgejo/workflows/test.yml
+++ b/actions/example-pull-request/.forgejo/workflows/test.yml
@@ -9,7 +9,7 @@ jobs:
   test:
     runs-on: docker
     container:
-      image: code.forgejo.org/oci/debian:bookworm
+      image: code.forgejo.org/oci/node:20-bookworm
       options: "--volume /srv/example-pull-request:/srv/example-pull-request"
 
     steps:
@@ -120,3 +120,20 @@ jobs:
           cat > $d/event <<'EOF'
           ${{ toJSON(github.event) }}
           EOF
+
+      - uses: https://code.forgejo.org/actions/checkout@v4
+      - name: checkout the default branch if pull_request_target
+        run: |
+          set -x
+          case $GITHUB_EVENT_NAME in
+            pull_request_target)
+              ! test -f file-unique-to-the-pr-branch
+              ;;
+            pull_request)
+              test -f file-unique-to-the-pr-branch
+              ;;
+            *)
+              echo unexpected event $GITHUB_EVENT_NAME
+              false
+              ;;
+          esac
diff --git a/actions/example-pull-request/run.sh b/actions/example-pull-request/run.sh
index 78bbf22..2a88afd 100755
--- a/actions/example-pull-request/run.sh
+++ b/actions/example-pull-request/run.sh
@@ -18,6 +18,7 @@ function setup() {
 	git config user.email root@example.com
 	git config user.name username
 	echo fork $PROOF >> README
+	touch file-unique-to-the-pr-branch
 	git add .
 	git commit -m 'fork change'
 	git push
@@ -32,6 +33,7 @@ function setup() {
 	git checkout -b other
 	git config user.email root@example.com
 	git config user.name username
+	touch file-unique-to-the-pr-branch
 	echo other $PROOF >> README
 	git add .
 	git commit -m 'other change'
diff --git a/actions/example-pull-request/runner-config.yaml b/actions/example-pull-request/runner-config.yaml
index e9f4aeb..5c3a6b3 100644
--- a/actions/example-pull-request/runner-config.yaml
+++ b/actions/example-pull-request/runner-config.yaml
@@ -10,7 +10,7 @@ runner:
   insecure: false
   fetch_timeout: 5s
   fetch_interval: 2s
-  labels: ["docker:docker://code.forgejo.org/oci/node:16-bullseye"]
+  labels: ["docker:docker://code.forgejo.org/oci/node:20-bookworm"]
 
 cache:
   enabled: false