1 files changed, 1 insertions, 0 deletions
diff --git a/class.c b/class.c
index 04e9dcbc2c..f87d2bdcca 100644
--- a/class.c
+++ b/class.c
@@ -826,6 +826,7 @@ rb_prepend_module(VALUE klass, VALUE module)
     origin = RCLASS_ORIGIN(klass);
     if (origin == klass) {
 	origin = class_alloc(T_ICLASS, klass);
+	OBJ_WB_UNPROTECT(origin); /* TODO: conservertive shading. Need more survery. */
 	RCLASS_SET_SUPER(origin, RCLASS_SUPER(klass));
 	RCLASS_SET_SUPER(klass, origin);
 	RCLASS_ORIGIN(klass) = origin;