diff --git a/lib/rb/ext/constants.h b/lib/rb/ext/constants.h
index 57df544..38b1d61 100644
--- a/lib/rb/ext/constants.h
+++ b/lib/rb/ext/constants.h
@@ -77,6 +77,7 @@
 extern ID native_qmark_method_id;
 
 extern ID fields_const_id;
+extern ID field_ids_const_id;
 extern ID transport_ivar_id;
 extern ID strict_read_ivar_id;
 extern ID strict_write_ivar_id;