1 files changed, 1 insertions, 1 deletions
diff --git a/src/vm.c b/src/vm.c
index e2b02a4ce..4aa9b9460 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -248,7 +248,7 @@ cipop(mrb_state *mrb)
     size_t len = (size_t)MRB_ENV_STACK_LEN(e);
     mrb_value *p = (mrb_value *)mrb_malloc(mrb, sizeof(mrb_value)*len);
 
-    e->cioff = -1;
+    MRB_ENV_UNSHARE_STACK(e);
     stack_copy(p, e->stack, len);
     e->stack = p;
   }