diff --git a/index.js b/index.js
index c331176c5488e12b3e812658cc3f51347d4ff973..127765d9c85217398ef9a0f24ac9d43c7cdb54b9 100644
--- a/index.js
+++ b/index.js
@@ -50,7 +50,7 @@ var bindingVisitor = {
         }
       }
 
-      state.undeclared[node.name] = true
+      Reflect.defineProperty(state.undeclared, node.name, { value: true, writable: true, enumerable: true, configurable: true })
     }
 
     if (state.wildcard &&