diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e645cfbd5..ad22fa61d 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -41,6 +41,7 @@ We have few hard rules, but we have some:
 - Printing to standard output or standard error (`stderr`, `stdout`, `std::cerr`, `std::cout`) in the core library is forbidden. This follows from the [Writing R Extensions](https://cran.r-project.org/doc/manuals/R-exts.html) manual which states that "Compiled code should not write to stdout or stderr".
 - Calls to `abort()` are forbidden in the core library. This follows from the [Writing R Extensions](https://cran.r-project.org/doc/manuals/R-exts.html) manual which states that "Under no circumstances should your compiled code ever call abort or exit".
 - All source code files (.h, .cpp) must be ASCII.
+- All C macros introduced in public headers need to be prefixed with either `SIMDJSON_` or `simdjson_`.
 
 Tools, tests and benchmarks are not held to these same strict rules.