diff --git a/src/oniguruma.js b/src/oniguruma.js
index bf14317..13a0bea 100644
--- a/src/oniguruma.js
+++ b/src/oniguruma.js
@@ -106,7 +106,8 @@ OnigString.prototype.toString = function (start, end) {
 }
 
 Object.defineProperty(OnigString.prototype, 'length', {
-  get() { return this.content.length }
+  get() { return this.content.length },
+  configurable: true
 })
 
 exports.OnigScanner = OnigScanner