diff --git a/test/phpunit.xml b/test/phpunit.xml
index 2c1078a7..cd4472b1 100644
--- a/test/phpunit.xml
+++ b/test/phpunit.xml
@@ -27,6 +27,9 @@
             <directory suffix=".php">../src/</directory>
         </include>
     </coverage>
+    <extensions>
+        <extension class="Ergebnis\PHPUnit\SlowTestDetector\Extension"/>
+    </extensions>
     <testsuites>
         <testsuite name="integration">
             <directory>Integration/</directory>