diff --git a/lib/utils.js b/lib/utils.js
index 6859abf1..4f0be041 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -99,9 +99,14 @@ exports.escapeXML = function (markup) {
     : String(markup)
       .replace(_MATCH_HTML, encode_char);
 };
-exports.escapeXML.toString = function () {
+
+// If the Object prototype is frozen, the "toString" property is non-writable. This means that any objects which inherit this property
+// cannot have the property changed using an assignment. If using strict mode, attempting that will cause an error. If not using strict
+// mode, attempting that will be silently ignored.
+// However, we can still explicitly shadow the prototype's "toString" property by defining a new "toString" property on this object.
+Object.defineProperty(exports.escapeXML, 'toString', function () {
   return Function.prototype.toString.call(this) + ';\n' + escapeFuncStr;
-};
+});
 
 /**
  * Naive copy of properties from one object to another.