diff --git a/7.md b/7.md
index 8530ced..8b58e50 100644
--- a/7.md
+++ b/7.md
@@ -82,6 +82,7 @@ Create a *functional test* to check that command chaining functionality works.
 Other Requirements
 ------------------
 - PSR-2
+- SOLID
 - http://symfony.com/doc/current/contributing/code/standards.html
 - All classes and methods should be documented with phpdoc, containing not only the list of parameters and their types,
 but also a short description of what the intended purpose of this method or class is.