diff --git a/composer.json b/composer.json
index 8c5dae4..b9dbf8e 100644
--- a/composer.json
+++ b/composer.json
@@ -26,7 +26,8 @@
         "phpcompatibility/php-compatibility": "^9.3",
         "symfony/filesystem": "^5",
         "symfony/service-contracts": "^2",
-        "symfony/translation-contracts": "^2"
+        "symfony/translation-contracts": "^2",
+        "yoast/phpunit-polyfills": "^1.0"
     },
     "scripts": {
         "lint": "@phpcs",
diff --git a/composer.lock b/composer.lock
index 19c7a95..ca3f34f 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "80da6ddc5c4660010e819f65d526e30d",
+    "content-hash": "ae9773c8cb26c9eff8c83b77a4751e56",
     "packages": [
         {
             "name": "onelogin/php-saml",
@@ -4702,6 +4702,69 @@
                 "wiki": "https://github.com/WordPress/WordPress-Coding-Standards/wiki"
             },
             "time": "2020-05-13T23:57:56+00:00"
+        },
+        {
+            "name": "yoast/phpunit-polyfills",
+            "version": "1.0.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/Yoast/PHPUnit-Polyfills.git",
+                "reference": "f014fb21c2b0038fd329515d59025af42fb98715"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/Yoast/PHPUnit-Polyfills/zipball/f014fb21c2b0038fd329515d59025af42fb98715",
+                "reference": "f014fb21c2b0038fd329515d59025af42fb98715",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.4",
+                "phpunit/phpunit": "^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0"
+            },
+            "require-dev": {
+                "php-parallel-lint/php-console-highlighter": "^0.5",
+                "php-parallel-lint/php-parallel-lint": "^1.3.0",
+                "yoast/yoastcs": "^2.1.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-main": "1.x-dev",
+                    "dev-develop": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "phpunitpolyfills-autoload.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "BSD-3-Clause"
+            ],
+            "authors": [
+                {
+                    "name": "Team Yoast",
+                    "email": "support@yoast.com",
+                    "homepage": "https://yoast.com"
+                },
+                {
+                    "name": "Contributors",
+                    "homepage": "https://github.com/Yoast/PHPUnit-Polyfills/graphs/contributors"
+                }
+            ],
+            "description": "Set of polyfills for changed PHPUnit functionality to allow for creating PHPUnit cross-version compatible tests",
+            "homepage": "https://github.com/Yoast/PHPUnit-Polyfills",
+            "keywords": [
+                "phpunit",
+                "polyfill",
+                "testing"
+            ],
+            "support": {
+                "issues": "https://github.com/Yoast/PHPUnit-Polyfills/issues",
+                "source": "https://github.com/Yoast/PHPUnit-Polyfills"
+            },
+            "time": "2021-08-09T16:28:08+00:00"
         }
     ],
     "aliases": [],
diff --git a/tests/phpunit/bootstrap.php b/tests/phpunit/bootstrap.php
index aa34f7c..f9c1911 100644
--- a/tests/phpunit/bootstrap.php
+++ b/tests/phpunit/bootstrap.php
@@ -10,6 +10,8 @@
 	$_tests_dir = '/tmp/wordpress-tests-lib';
 }
 
+define( 'WP_TESTS_PHPUNIT_POLYFILLS_PATH', __DIR__ . '/../../vendor/yoast/phpunit-polyfills/phpunitpolyfills-autoload.php' );
+
 // Give access to tests_add_filter() function.
 require_once $_tests_dir . '/includes/functions.php';