diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e715a8f0ba292c31314e7f4fbca9ddaf9f8bbeb0..513fb27f73bbbaf8808d09971beae9b4d7457d9e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -123,7 +123,8 @@ below this would be fantastic.
   }
   ```
 - **Don't use preprocessor directives and macros unless there is no viable
-  alternative.** The exception to this is header guards inside your `.h` files,
+  alternative.**
+- However, please make sure you do have a header guard inside your `.h` files,
   which you should be sure to include in any headers you contribute.
 - Use one `.cpp` and `.h` file per C++ class, and try to keep `inline` header
   code to a minimum (unless performance is a major factor).