diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index bf1eaa689..91b97f4e1 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -127,6 +127,7 @@ Style conventions for stub files are different from PEP 8. The general
 rule is that they should be as concise as possible.  Specifically:
 * there is no line length limit;
 * prefer long lines over elaborate indentation;
+* all function bodies should be empty;
 * prefer ``...`` over ``pass``;
 * prefer ``...`` on the same line as the class/function signature;
 * avoid vertical whitespace between consecutive module-level functions,