diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 7af1b27..bb1e62c 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -1,11 +1,8 @@
 name: CI
-on:
-  push:
-  pull_request:
-  workflow_dispatch:
+on: [push, pull_request]
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
       - uses: hashicorp/setup-terraform@v1.2.1