diff --git a/cookbook/testing/doctrine.rst b/cookbook/testing/doctrine.rst
index b4f1cda682a..75b986cdfd8 100644
--- a/cookbook/testing/doctrine.rst
+++ b/cookbook/testing/doctrine.rst
@@ -64,3 +64,7 @@ which makes all of this quite easy::
             $this->em->close();
         }
     }
+
+.. note::
+
+    Depending on your PHP version, you might need to call ``gc_collect_cycles()`` after closing the connection.