diff --git a/phpunit.xml b/phpunit.xml
index 05c6692..2bebb13 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -17,4 +17,9 @@
       <directory suffix="Test.php">tests</directory>
     </testsuite>
   </testsuites>
+  <source>
+    <include>
+      <directory suffix=".php">src</directory>
+    </include>
+  </source>
 </phpunit>