diff --git a/internal.h b/internal.h
index 949c6f8a42..dc3862323a 100644
--- a/internal.h
+++ b/internal.h
@@ -390,6 +390,8 @@ struct RRational {
 };
 
 #define RRATIONAL(obj) (R_CAST(RRational)(obj))
+#define RRATIONAL_SET_NUM(rat, n) RB_OBJ_WRITE((rat), &((struct RRational *)(rat))->num,(n))
+#define RRATIONAL_SET_DEN(rat, d) RB_OBJ_WRITE((rat), &((struct RRational *)(rat))->den,(d))
 
 struct RFloat {
     struct RBasic basic;