diff --git a/derive_builder_core/src/builder_field.rs b/derive_builder_core/src/builder_field.rs
index ec7567b4..209ec84e 100644
--- a/derive_builder_core/src/builder_field.rs
+++ b/derive_builder_core/src/builder_field.rs
@@ -117,6 +117,7 @@ impl<'a> BuilderField<'a> {
 
 /// Helper macro for unit tests. This is _only_ public in order to be accessible
 /// from doc-tests too.
+#[cfg(test)] // This contains a Box::leak, so is suitable only for tests
 #[doc(hidden)]
 #[macro_export]
 macro_rules! default_builder_field {