diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5efea0a2f..bd96d2695 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,14 +27,14 @@ jobs:
           - ubuntu-latest
           - windows-latest
         php:
-          - '7.2'
-          - '7.3'
-          - '7.4'
-          - '8.0'
-          - '8.1'
-          - '8.2'
-          - '8.3'
-          - '8.4'
+          - { version: '7.2', phpunit: '8.5.*' }
+          - { version: '7.3', phpunit: '9.6.*' }
+          - { version: '7.4', phpunit: '9.6.*' }
+          - { version: '8.0', phpunit: '9.6.*' }
+          - { version: '8.1', phpunit: '9.6.*' }
+          - { version: '8.2', phpunit: '9.6.*' }
+          - { version: '8.3', phpunit: '9.6.*' }
+          - { version: '8.4', phpunit: '9.6.*' }
         dependencies:
           - lowest
           - highest
@@ -48,7 +48,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
-          php-version: ${{ matrix.php }}
+          php-version: ${{ matrix.php.version }}
           coverage: xdebug
 
       - name: Setup Problem Matchers for PHPUnit
@@ -63,13 +63,16 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ${{ steps.composer-cache.outputs.directory }}
-          key: ${{ runner.os }}-${{ matrix.php }}-composer-${{ matrix.dependencies }}-${{ hashFiles('**/composer.lock') }}
-          restore-keys: ${{ runner.os }}-${{ matrix.php }}-${{ matrix.dependencies }}-composer-
+          key: ${{ runner.os }}-${{ matrix.php.version }}-composer-${{ matrix.dependencies }}-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-${{ matrix.php.version }}-${{ matrix.dependencies }}-composer-
 
       # These dependencies are not used running the tests but can cause deprecation warnings so we remove them before running the tests
       - name: Remove unused dependencies
         run: composer remove vimeo/psalm phpstan/phpstan friendsofphp/php-cs-fixer  --dev --no-interaction --no-update
 
+      - name: Set phpunit/phpunit version constraint
+        run: composer require phpunit/phpunit:'${{ matrix.php.phpunit }}' --dev --no-interaction --no-update
+
       - name: Install highest dependencies
         run: composer update --no-progress --no-interaction --prefer-dist
         if: ${{ matrix.dependencies == 'highest' }}
@@ -89,4 +92,4 @@ jobs:
 
       - name: Check benchmarks
         run: vendor/bin/phpbench run --revs=1 --iterations=1
-        if: ${{ matrix.dependencies == 'highest' && matrix.php == '8.2' }}
+        if: ${{ matrix.dependencies == 'highest' && matrix.php.version == '8.2' }}
diff --git a/composer.json b/composer.json
index ed9bc4792..0be4a6531 100644
--- a/composer.json
+++ b/composer.json
@@ -38,7 +38,7 @@
         "monolog/monolog": "^1.6|^2.0|^3.0",
         "phpbench/phpbench": "^1.0",
         "phpstan/phpstan": "^1.3",
-        "phpunit/phpunit": "^9.4",
+        "phpunit/phpunit": "^8.5|^9.6",
         "symfony/phpunit-bridge": "^5.2|^6.0|^7.0",
         "vimeo/psalm": "^4.17"
     },