Fill in missing cfgs on private code
diff --git a/src/lib.rs b/src/lib.rs
index 1a4abbe..1d6c60c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -590,6 +590,7 @@
 
 ////////////////////////////////////////////////////////////////////////////////
 
+#[cfg(any(feature = "parsing", feature = "full", feature = "derive"))]
 #[allow(non_camel_case_types)]
 struct private;