diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index dda484fabd..00c9ba42ce 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -42,6 +42,7 @@ Nobody is perfect, and sometimes we mess things up. That said, here are some goo
 * The first line of the commit message should have the format "Category: Brief description of what's being changed". The "category" can be a subdirectory, but also something like "POSIX compliance" or "ClassName". Whatever seems logical.
 * Write your commit messages in proper English, with care and punctuation.
 * Squash your commits when making revisions after a patch review.
+* Add your personal copyright line to files when making substantive changes. (Optional but encouraged!)
 
 **Don't:**