diff --git a/README.md b/README.md
index 0dca93cf..a45213fc 100644
--- a/README.md
+++ b/README.md
@@ -21,8 +21,6 @@ Example of obfuscated code: [gist.github.com](https://gist.github.com/sanex3339/
 * Gulp: [gulp-javascript-obfuscator](https://github.com/javascript-obfuscator/gulp-javascript-obfuscator)
 * Grunt: [grunt-contrib-obfuscator](https://github.com/javascript-obfuscator/grunt-contrib-obfuscator)
 
-[![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=6SDRM5JRMGH9Y)
-
 [![npm version](https://badge.fury.io/js/javascript-obfuscator.svg)](https://badge.fury.io/js/javascript-obfuscator)
 [![Build Status](https://travis-ci.org/javascript-obfuscator/javascript-obfuscator.svg?branch=master)](https://travis-ci.org/javascript-obfuscator/javascript-obfuscator)
 [![Coverage Status](https://coveralls.io/repos/github/javascript-obfuscator/javascript-obfuscator/badge.svg?branch=master)](https://coveralls.io/github/javascript-obfuscator/javascript-obfuscator?branch=master)
diff --git a/src/utils/RandomGeneratorUtils.ts b/src/utils/RandomGeneratorUtils.ts
index 5e5af761..419d5c89 100644
--- a/src/utils/RandomGeneratorUtils.ts
+++ b/src/utils/RandomGeneratorUtils.ts
@@ -16,7 +16,7 @@ export class RandomGeneratorUtils {
     /**
      * @type {Set<string>}
      */
-    public static randomVariableNameSet: Set <string> = new Set();
+    public static readonly randomVariableNameSet: Set <string> = new Set();
 
     /**
      * @type {Chance.Chance | Chance.SeededChance}