diff --git a/packages/google-cloud-bigquery-reservation/scripts/decrypt-secrets.sh b/packages/google-cloud-bigquery-reservation/scripts/decrypt-secrets.sh
index ff599eb2af25..21f6d2a26d90 100755
--- a/packages/google-cloud-bigquery-reservation/scripts/decrypt-secrets.sh
+++ b/packages/google-cloud-bigquery-reservation/scripts/decrypt-secrets.sh
@@ -20,14 +20,27 @@ ROOT=$( dirname "$DIR" )
 # Work from the project root.
 cd $ROOT
 
+# Prevent it from overriding files.
+# We recommend that sample authors use their own service account files and cloud project.
+# In that case, they are supposed to prepare these files by themselves.
+if [[ -f "testing/test-env.sh" ]] || \
+       [[ -f "testing/service-account.json" ]] || \
+       [[ -f "testing/client-secrets.json" ]]; then
+    echo "One or more target files exist, aborting."
+    exit 1
+fi
+
 # Use SECRET_MANAGER_PROJECT if set, fallback to cloud-devrel-kokoro-resources.
 PROJECT_ID="${SECRET_MANAGER_PROJECT:-cloud-devrel-kokoro-resources}"
 
 gcloud secrets versions access latest --secret="python-docs-samples-test-env" \
+       --project="${PROJECT_ID}" \
        > testing/test-env.sh
 gcloud secrets versions access latest \
        --secret="python-docs-samples-service-account" \
+       --project="${PROJECT_ID}" \
        > testing/service-account.json
 gcloud secrets versions access latest \
        --secret="python-docs-samples-client-secrets" \
-       > testing/client-secrets.json
\ No newline at end of file
+       --project="${PROJECT_ID}" \
+       > testing/client-secrets.json
diff --git a/packages/google-cloud-bigquery-reservation/synth.metadata b/packages/google-cloud-bigquery-reservation/synth.metadata
index f9298ddc6266..ebfa71dbe8b7 100644
--- a/packages/google-cloud-bigquery-reservation/synth.metadata
+++ b/packages/google-cloud-bigquery-reservation/synth.metadata
@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "d91dd8aac77f7a9c5506c238038a26fa4f9e361e"
+        "sha": "d302f93d7f47e2852e585ac35ab2d15585717ec0"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "d91dd8aac77f7a9c5506c238038a26fa4f9e361e"
+        "sha": "d302f93d7f47e2852e585ac35ab2d15585717ec0"
       }
     }
   ],