diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 17eed43c5..c8df2d058 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -153,6 +153,8 @@ uv sync
   justification for bypassing the check.
 * When using `# type: ignore` to suppress a mypy warning, include a comment explaining the
   justification for bypassing the check.
+* Don't use unicode characters in the codebase. ASCII-only is preferred for compatibility or
+  readability reasons.
 
 ## Common Tasks