diff --git a/.travis.yml b/.travis.yml
index e1f556b..8e6e420 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,6 +20,8 @@ matrix:
       dist: bionic
     - php: 7.4
       dist: bionic
+    - php: 8.0snapshot
+      dist: bionic
 
 install:
   - composer install --prefer-dist --no-interaction --no-progress
diff --git a/composer.json b/composer.json
index f8b40f8..56c91b5 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
         "ext-mbstring": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35"
+        "phpunit/phpunit": "^4.8.35|^9.0"
     },
     "autoload": {
         "psr-0": {"Parsedown": ""}
diff --git a/test/CommonMarkTestStrict.php b/test/CommonMarkTestStrict.php
index 3837738..9a007e2 100644
--- a/test/CommonMarkTestStrict.php
+++ b/test/CommonMarkTestStrict.php
@@ -1,11 +1,13 @@
 <?php
 
+use PHPUnit\Framework\TestCase;
+
 /**
  * Test Parsedown against the CommonMark spec
  *
  * @link http://commonmark.org/ CommonMark
  */
-class CommonMarkTestStrict extends PHPUnit_Framework_TestCase
+class CommonMarkTestStrict extends TestCase
 {
     const SPEC_URL = 'https://raw.githubusercontent.com/jgm/CommonMark/master/spec.txt';