diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index dd6f7f7..97e0c85 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -31,6 +31,12 @@ jobs:
           tools: composer:v2
           coverage: none
 
+      - name: Setup tests for PHP < 7.4
+        if: matrix.php < 7.4
+        run: |
+          composer require --dev 'phpunit/phpunit:^4.8.36 || ^5.7.21 || ^6 || ^7' --no-update
+          sed -i 's/: void//g' tests/*.php
+
       - name: Install dependencies
         run: composer install --prefer-dist --no-interaction --no-progress
 
diff --git a/composer.json b/composer.json
index 951f04e..f4e8af7 100644
--- a/composer.json
+++ b/composer.json
@@ -44,7 +44,7 @@
         "pear/net_socket": "~1.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35 || ^5.7.21 || ^6 || ^7"
+        "phpunit/phpunit": "^4.8.35 || ^5.7.21 || ^6 || ^7 || ^9"
     },
     "suggest": {
         "pear/auth_sasl": "Install optionally via your project's composer.json"
diff --git a/tests/SieveTest.php b/tests/SieveTest.php
index 8e208f1..58e4bbe 100644
--- a/tests/SieveTest.php
+++ b/tests/SieveTest.php
@@ -57,7 +57,7 @@ class SieveTest extends PHPUnit\Framework\TestCase
     // contains the object handle of the string class
     protected $fixture;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         if (!file_exists(dirname(__FILE__) . '/config.php')) {
             $this->markTestSkipped('Test configuration incomplete. Copy config.php.dist to config.php.');
@@ -74,7 +74,7 @@ protected function setUp()
             'test script4' => file_get_contents(dirname(__FILE__) . '/largescript.siv'));
     }
     
-    protected function tearDown()
+    protected function tearDown(): void
     {
         // Delete the instance.
         unset($this->fixture);