diff --git a/lib/runtime-c-api/README.md b/lib/runtime-c-api/README.md
index 8ce84a130..06e545bf7 100644
--- a/lib/runtime-c-api/README.md
+++ b/lib/runtime-c-api/README.md
@@ -105,6 +105,10 @@ int main()
 
 # Testing
 
+Tests are run using the release build of the library.  If you make
+changes or compile with non-default features, please ensure you
+rebuild in release mode for the tests to see the changes.
+
 The tests can be run via `cargo test`, such as:
 
 ```sh