diff --git a/composer.json b/composer.json
index 9d53697..3ede0b0 100644
--- a/composer.json
+++ b/composer.json
@@ -20,8 +20,7 @@
         }
     },
     "require-dev": {
-      "phpunit/phpunit": "^5.5||^6.0||^7.0||^8.0||^9.0",
-      "phpdocumentor/phpdocumentor": "^2.9",
+      "phpunit/phpunit": "^9.0",
       "mockery/mockery": "^1.0"
 
     },
diff --git a/tests/GhostscriptTest.php b/tests/GhostscriptTest.php
index 9f72ab0..f19731a 100644
--- a/tests/GhostscriptTest.php
+++ b/tests/GhostscriptTest.php
@@ -42,7 +42,7 @@
  */
 class GhostscriptTest extends TestCase
 {
-    public function setup()
+    public function setup(): void
     {
         Ghostscript::setGsPath();
     }