diff --git a/lib/rb/ext/constants.h b/lib/rb/ext/constants.h
index e540234..1922fb1 100644
--- a/lib/rb/ext/constants.h
+++ b/lib/rb/ext/constants.h
@@ -60,6 +60,8 @@
 
 extern ID fields_const_id;
 extern ID transport_ivar_id;
+extern ID strict_read_ivar_id;
+extern ID strict_write_ivar_id;
 
 extern VALUE type_sym;
 extern VALUE name_sym;