diff --git a/lib/rb/ext/constants.h b/lib/rb/ext/constants.h
index 57df544..9ea00d2 100644
--- a/lib/rb/ext/constants.h
+++ b/lib/rb/ext/constants.h
@@ -74,6 +74,7 @@
 extern ID skip_method_id;
 extern ID write_method_id;
 extern ID read_all_method_id;
+extern ID read_into_buffer_method_id;
 extern ID native_qmark_method_id;
 
 extern ID fields_const_id;