diff --git a/.gitattributes b/.gitattributes
index c2a942e..cb84257 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -3,4 +3,5 @@
 /.gitignore export-ignore
 /bin/build.php export-ignore
 /phpunit.xml.dist export-ignore
+/phpunit.xml.legacy export-ignore
 /tests/ export-ignore
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cf5fe14..e6e791f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,6 +28,9 @@ jobs:
           coverage: xdebug
       - run: composer install
       - run: vendor/bin/phpunit --coverage-text
+        if: ${{ matrix.php >= 7.3 }}
+      - run: vendor/bin/phpunit --coverage-text -c phpunit.xml.legacy
+        if: ${{ matrix.php < 7.3 }}
       - run: composer build
 
   PHPUnit-hhvm:
diff --git a/composer.json b/composer.json
index 107b7b2..e4185a2 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,7 @@
     },
     "require-dev": {
         "clue/phar-composer": "^1.3",
-        "phpunit/phpunit": "^4.8.36"
+        "phpunit/phpunit": "^9.5 || ^5.7 || ^4.8.36"
     },
     "autoload": {
         "psr-0": { "Clue\\GraphComposer": "src/" }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 7d716bb..2aefcaa 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,14 +1,20 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit colors="true" bootstrap="vendor/autoload.php">
+<!-- PHPUnit configuration file with new format for PHPUnit 9.5+ -->
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         cacheResult="false"
+         colors="true"
+         convertDeprecationsToExceptions="true">
     <testsuites>
         <testsuite name="GraphComposer Test Suite">
             <directory>./tests/</directory>
         </testsuite>
     </testsuites>
-    <filter>
-        <whitelist>
-            <directory>./src</directory>
-        </whitelist>
-    </filter>
-</phpunit>
\ No newline at end of file
+    <coverage>
+        <include>
+            <directory>./src/</directory>
+        </include>
+    </coverage>
+</phpunit>
diff --git a/phpunit.xml.legacy b/phpunit.xml.legacy
new file mode 100644
index 0000000..601ecb5
--- /dev/null
+++ b/phpunit.xml.legacy
@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!-- PHPUnit configuration file with old format before PHPUnit 9 -->
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/4.8/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         colors="true">
+    <testsuites>
+        <testsuite name="GraphComposer Test Suite">
+            <directory>./tests/</directory>
+        </testsuite>
+    </testsuites>
+    <filter>
+        <whitelist>
+            <directory>./src/</directory>
+        </whitelist>
+    </filter>
+</phpunit>
diff --git a/tests/AppTest.php b/tests/AppTest.php
index 7f45f8d..371f6ae 100644
--- a/tests/AppTest.php
+++ b/tests/AppTest.php
@@ -1,8 +1,9 @@
 <?php
 
 use Clue\GraphComposer\App;
+use PHPUnit\Framework\TestCase;
 
-class AppTest extends PHPUnit_Framework_TestCase
+class AppTest extends TestCase
 {
     public function testVersionReturnsDev()
     {
diff --git a/tests/GraphComposerTest.php b/tests/GraphComposerTest.php
index 32ff41c..ffb0151 100644
--- a/tests/GraphComposerTest.php
+++ b/tests/GraphComposerTest.php
@@ -1,8 +1,9 @@
 <?php
 
 use Clue\GraphComposer\Graph\GraphComposer;
-use Graphp\GraphViz\GraphViz;
 use Fhaculty\Graph\Graph;
+use Graphp\GraphViz\GraphViz;
+use PHPUnit\Framework\TestCase;
 
 class GraphVizMockDisplay extends GraphViz
 {
@@ -31,7 +32,7 @@ public function setFormat($format)
     }
 }
 
-class GraphTest extends PHPUnit_Framework_TestCase
+class GraphTest extends TestCase
 {
     public function testCreateGraph()
     {