diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index b3023c94bdcd60a0588afde0790ca7f19d8d1ecb..6b7ab23959ff8d1235cd2c2343fb0323eabcafc4 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -60,6 +60,8 @@ type(scope): short description
 
 Common types: `feat`, `fix`, `docs`, `test`, `ci`, `chore`.
 
+Keep commit messages to 40 characters or fewer.
+
 Examples:
 ```
 feat(compose): add CC/BCC field support