diff --git a/src/class.c b/src/class.c
index 6aa9c1881..c2bffeaf9 100644
--- a/src/class.c
+++ b/src/class.c
@@ -950,8 +950,7 @@ find_visibility_scope(mrb_state *mrb, const struct RClass *c, int n, mrb_callinf
   if (c == NULL) c = mrb_vm_ci_target_class(ci);
 
   if (check_visibility_break(p, c, ci, NULL)) {
-    mrb_assert(ci->u.env);
-    *ep = (ci->u.env->tt == MRB_TT_ENV ? ci->u.env : NULL);
+    *ep = (ci->u.env && ci->u.env->tt == MRB_TT_ENV) ? ci->u.env : NULL;
     *cp = ci;
     return;
   }