diff --git a/.github/workflows/ubuntu18_pr.yaml b/.github/workflows/ubuntu18_pr.yaml
index 8b5489c..cf29615 100644
--- a/.github/workflows/ubuntu18_pr.yaml
+++ b/.github/workflows/ubuntu18_pr.yaml
@@ -1,69 +1,64 @@
 name: "Test on Ubuntu Github Runners"
 
 on: [push, pull_request]
 
 jobs:
   Acceptance:
     strategy:
       fail-fast: false
       matrix:
         platform:
           - ubuntu-16.04
           - ubuntu-18.04
           - ubuntu-20.04
         collection:
-          - puppet5
-          - puppet6
+          - puppet6-nightly
           - puppet7-nightly
-        exclude:
-          # newer OS not supported on older agent
-          - platform: ubuntu-20.04
-            collection: puppet5
 
     runs-on: ${{ matrix.platform }}
 
     steps:
       - name: Checkout Source
         uses: actions/checkout@v2
 
       - name: Activate Ruby 2.7
         uses: actions/setup-ruby@v1
         with:
           ruby-version: "2.7"
 
       - name: Cache gems
         uses: actions/cache@v2
         with:
           path: vendor/gems
           key: ${{ runner.os }}-pr-${{ hashFiles('**/Gemfile') }}
           restore-keys: |
             ${{ runner.os }}-pr-
             ${{ runner.os }}-
 
       - name: Prepare inventory file
         run: |
           cat <<EOF >> inventory.yaml
           ---
           version: 2
           groups:
           - name: local
             targets:
             - uri: litmus_localhost
               config:
                 transport: local
           - name: ssh_nodes
             targets: []
           - name: winrm_nodes
             targets: []
           EOF
 
       - name: Install gems and puppet agent
         run: |
           bundle install
           sudo -u root env "PATH=$PATH" bundle exec rake 'litmus:install_agent[${{ matrix.collection }}]'
 
       - name: Install module
         run: bundle exec rake 'litmus:install_module'
 
       - name: Run acceptance tests
         run: sudo -u root env "PATH=$PATH" bundle exec rake 'litmus:acceptance:localhost'