Avoid unsharing stack if env refers top-level; ref #3643

1 files changed, 1 insertions, 0 deletions

diff --git a/src/vm.c b/src/vm.c
index b3e06cb54..4d7fc9720 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -264,6 +264,7 @@ mrb_env_unshare(mrb_state *mrb, struct REnv *e)
   mrb_value *p;
 
   if (!MRB_ENV_STACK_SHARED_P(e)) return;
+  if (e->cioff == 0 && e->cxt.c == mrb->root_c) return;
   MRB_ENV_UNSHARE_STACK(e);
   if (!e->c) {
     /* save block argument position (negated) */