diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 5ccbf7c87d..71b25e1900 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -67,6 +67,7 @@ After that, there are several rules you should follow when a new pull request is
   - Change UI assets version, present in [package.json](package.json) file. Minor if it is a bugfixing or a small feature, major when it is a big change.
 - Our linter machine, [Hound](https://houndci.com/), should not trigger any warnings about your changes.
 - All tests should pass, both for JS and Ruby.
+- The number of modified lines should not exceed 300. If so, please split it into smaller PRs to make it easier to review.
 
 ## Development environment accessories