diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index dc4576e..2558609 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -38,7 +38,9 @@ jobs:
 
     - name: Install dependencies
       if: steps.composer-cache.outputs.cache-hit != 'true'
-      run: composer update --prefer-dist --no-progress --no-suggest --prefer-${{ matrix.setup || 'stable' }} ${{ matrix.php >= 8 && '--ignore-platform-req=php' || '' }}
+      run: |
+        ${{ matrix.php >= 8.1 && 'composer require --no-update phpunit/phpunit:^8.5.14 --no-interaction;' || '' }}
+        composer update --prefer-dist --no-progress --no-suggest --prefer-${{ matrix.setup || 'stable' }} ${{ matrix.php >= 8 && '--ignore-platform-req=php' || '' }}
 
     - name: Run test suite
       run: vendor/bin/phpunit --no-coverage
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 327b5be..44b9898 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -16,6 +16,9 @@
             <directory suffix=".php">src/</directory>
         </whitelist>
     </filter>
+    <php>
+        <ini name="date.timezone" value="UTC"/>
+    </php>
     <logging>
         <log type="tap" target="build/report.tap"/>
         <log type="junit" target="build/report.junit.xml"/>
diff --git a/tests/OpeningHoursCustomClassTest.php b/tests/OpeningHoursCustomClassTest.php
index 3a9067c..5d28bdd 100644
--- a/tests/OpeningHoursCustomClassTest.php
+++ b/tests/OpeningHoursCustomClassTest.php
@@ -10,11 +10,6 @@
 
 class OpeningHoursCustomClassTest extends TestCase
 {
-    protected function setUp()
-    {
-        date_default_timezone_set('UTC');
-    }
-
     /** @test */
     public function it_can_use_immutable_date_time()
     {
diff --git a/tests/OpeningHoursTest.php b/tests/OpeningHoursTest.php
index da8dd1b..b81cd21 100644
--- a/tests/OpeningHoursTest.php
+++ b/tests/OpeningHoursTest.php
@@ -14,11 +14,6 @@
 
 class OpeningHoursTest extends TestCase
 {
-    protected function setUp()
-    {
-        date_default_timezone_set('UTC');
-    }
-
     /** @test */
     public function it_can_return_the_opening_hours_for_a_regular_week()
     {