diff --git a/.github/workflows/system-test.yaml b/.github/workflows/system-test.yaml
index 63f3726..eea6bf9 100644
--- a/.github/workflows/system-test.yaml
+++ b/.github/workflows/system-test.yaml
@@ -1,10 +1,14 @@
 on:
-  push:
+  pull_request:
     paths: 
       - .github/workflows/system-test.yaml
       - system_test/**
       - pkg/**
       - go.*
+  push:
+    # for go mod tidy
+    branches: [master]
+    paths: [go.*]
 jobs:
   system-test:
     # https://help.github.com/en/actions/automating-your-workflow-with-github-actions/software-installed-on-github-hosted-runners#ubuntu-1804-lts