1 files changed, 1 insertions, 1 deletions
diff --git a/class.c b/class.c
index 42c27b5f32..73e7003d6a 100644
--- a/class.c
+++ b/class.c
@@ -939,7 +939,7 @@ rb_prepend_module(VALUE klass, VALUE module)
 	OBJ_WB_UNPROTECT(origin); /* TODO: conservative shading. Need more survey. */
 	RCLASS_SET_SUPER(origin, RCLASS_SUPER(klass));
 	RCLASS_SET_SUPER(klass, origin);
-	RCLASS_ORIGIN(klass) = origin;
+	RB_OBJ_WRITE(klass, &RCLASS_ORIGIN(klass), origin);
 	RCLASS_M_TBL(origin) = RCLASS_M_TBL(klass);
 	RCLASS_M_TBL_INIT(klass);
 	st_foreach(RCLASS_M_TBL(origin), move_refined_method,