diff --git a/CODE_STYLE.md b/CODE_STYLE.md
index 2eaac05c9..d3337b16f 100644
--- a/CODE_STYLE.md
+++ b/CODE_STYLE.md
@@ -16,6 +16,8 @@ Any exception or additions specific to our project are documented below.
 
 * Try to avoid acronyms and abbreviations.
 
+* All state variables should be private.
+
 * Private state variables should have an underscore prefix.
 
     ```