diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md
index 9a72d74..b581f7e 100644
--- a/CppCoreGuidelines.md
+++ b/CppCoreGuidelines.md
@@ -2080,6 +2080,13 @@ This is usually a very good thing.
 
 Don't try to make all functions `constexpr`. Most computation is best done at run time.
 
+##### Note
+
+Any API that may eventually depend on high-level runtime configuration or
+business logic should not be made `constexpr`. Such customization can not be
+evaluated by the compiler, and any `constexpr` functions that depend upon that
+API will have to be refactored or drop `constexpr`.
+
 ##### Enforcement
 
 Impossible and unnecessary.