diff --git a/.github/workflows/phpunit-tests.yml b/.github/workflows/phpunit-tests.yml
index 4e206fa634..86ecd524b7 100644
--- a/.github/workflows/phpunit-tests.yml
+++ b/.github/workflows/phpunit-tests.yml
@@ -124,27 +124,35 @@ jobs:
   # - Submit the test results to the WordPress.org host test results.
   # - todo: Configure Slack notifications for failing tests.
   test-php:
-    name: ${{ matrix.php }}${{ matrix.memcached && ' with memcached' || '' }} on ${{ matrix.os }}
+    name: ${{ matrix.php }}${{ matrix.multisite && ' multisite' || '' }}${{ matrix.memcached && ' with memcached' || '' }} on ${{ matrix.os }}
     needs: setup-wordpress
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        php: [ '8.0', '7.4', '7.3', '7.2', '7.1', '7.0', '5.6.20' ]
+        php: [ '5.6.20', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0' ]
         os: [ ubuntu-latest ]
         memcached: [ false ]
+        multisite: [ false, true ]
         include:
-          # Include job for PHP 7.4 with memcached.
+          # Include jobs for PHP 7.4 with memcached.
           - php: '7.4'
             os: ubuntu-latest
             memcached: true
+            multisite: false
+          - php: '7.4'
+            os: ubuntu-latest
+            memcached: true
+            multisite: true
           # Report the results of the PHP 7.4 without memcached job.
           - php: '7.4'
             os: ubuntu-latest
             memcached: false
+            multisite: false
             report: true
     env:
       LOCAL_PHP: ${{ matrix.php }}-fpm
       LOCAL_PHP_MEMCACHED: ${{ matrix.memcached }}
+      PHPUNIT_CONFIG: ${{ matrix.multisite && 'tests/phpunit/multisite.xml' || 'phpunit.xml.dist' }}
 
     steps:
       - name: Configure environment variables
@@ -249,24 +257,21 @@ jobs:
         run: npm run env:install
 
       - name: Run PHPUnit tests
-        run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c phpunit.xml.dist
+        run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c ${{ env.PHPUNIT_CONFIG }}
 
       - name: Run AJAX tests
-        run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c phpunit.xml.dist --group ajax
-
-      - name: Run tests as a multisite install
-        run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c tests/phpunit/multisite.xml
-
-      - name: Run AJAX tests as a multisite install
-        run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c tests/phpunit/multisite.xml --group ajax
+        run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c ${{ env.PHPUNIT_CONFIG }} --group ajax
 
       - name: Run ms-files tests as a multisite install
+        if: ${{ matrix.multisite }}
         run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c tests/phpunit/multisite.xml --group ms-files
 
       - name: Run external HTTP tests
+        if: ${{ ! matrix.multisite }}
         run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c phpunit.xml.dist --group external-http
 
       - name: Run REST API tests
+        if: ${{ ! matrix.multisite }}
         run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c phpunit.xml.dist --group restapi-jsclient
 
       # __fakegroup__ is excluded to force PHPUnit to ignore the <exclude> settings in phpunit.xml.dist.