diff --git a/composer.json b/composer.json
index 107b7b2..976d2c3 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": "^7.5 || ^5.7 || ^4.8.36"
     },
     "autoload": {
         "psr-0": { "Clue\\GraphComposer": "src/" }
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()
     {