diff --git a/symbol.c b/symbol.c
index cd67c53663..9917795190 100644
--- a/symbol.c
+++ b/symbol.c
@@ -400,6 +400,9 @@ get_id_entry(rb_id_serial_t num, const enum id_entry_type t)
 }
 
 static inline ID
+#ifdef __GNUC__
+__attribute__((unused))
+#endif
 rb_id_serial_to_id(rb_id_serial_t num)
 {
     if (is_notop_id((ID)num)) {