diff --git a/src/vm.c b/src/vm.c
index 4fc929e2a..732cbe2a8 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -395,6 +395,7 @@ mrb_env_unshare(mrb_state *mrb, struct REnv *e, mrb_bool noraise)
     stack_copy(p, e->stack, len);
     e->stack = p;
     MRB_ENV_CLOSE(e);
+    mrb_write_barrier(mrb, (struct RBasic*)e);
     return TRUE;
   }
   else {