diff --git .github/workflows/unit-tests.yml .github/workflows/unit-tests.yml
index bb3cd9d41..3321075d8 100644
--- .github/workflows/unit-tests.yml
+++ .github/workflows/unit-tests.yml
@@ -58,6 +58,9 @@ jobs:
         with:
           composer-options: "--ignore-platform-reqs"
 
+      - name: Adjust wp-phpunit version
+        run: if [ ${{ env.WP_VERSION }} == '5.4' ]; then composer require --dev "wp-phpunit/wp-phpunit:5.4"; fi
+
       - name: Cache node modules
         uses: actions/cache@v2
         env:
diff --git composer.json composer.json
index 92645a69f..84de36797 100644
--- composer.json
+++ composer.json
@@ -35,7 +35,7 @@
 		"dealerdirect/phpcodesniffer-composer-installer": "^0.7.1",
 		"squizlabs/php_codesniffer" : "^3.5.4",
 		"wp-coding-standards/wpcs": "*",
-		"wp-phpunit/wp-phpunit": "^5.7",
+		"wp-phpunit/wp-phpunit": "^5.8",
 		"phpunit/phpunit": "^7.5"
 	}
 }